The effects of cool and variable temperatures on the hatch date,growth and overwinter mortality of a warmwater fish in small coastal embayments of Lake Ontario

Little is known about the ecology of warmwater fish in small coastal embayments (< 32 ha) where temperatures are lowered by exchange with the adjacent lake. Using pumpkinseed (Lepomis gibbous) as a model warmwater fish, we compare hatch dates and overwinter survival in two embayments with higher and lower amounts of cold-water input from Lake Ontario, in a warmer and cooler year. In 2007, the embayments differed by approximately 2–5 °C until late-July. In that year, temperatures in the cooler embayment delayed hatching times until July 18–August 20, approximately eight weeks later (May 24–August 20) than in the warmer embayment. Almost all offspring in the cooler embayment were likely too small to survive the winter. In 2008 both embayments had similar temperatures. In that year, pumpkinseed started hatching in early-June, and most were likely large enough to survive the winter. The findings from the two intensively sampled embayments were confirmed with a 21-year fish monitoring dataset; adult pumpkinseed were captured in the littoral zone of warm embayments 6–8 weeks earlier than in cooler embayments. Relative to pumpkinseed in the small inland lakes of eastern and central Ontario, spawning is delayed by at least two weeks in coastal embayments. Using water temperatures as a surrogate for growth, we calculated that only 5 of the 17 embayments for which we have temperature records were able to consistently produce successfully overwintering age-0 fish. Nevertheless, we found pumpkinseed age ≥ 1 in embayments too cold to produce age-0 pumpkinseed, suggesting immigration from warmer embayments.     

Thermal habitat characteristics for warmwater fishes in coastal embayments of Lake Ontario

Along 40 km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (4.38-848 × 10³ m²) have been constructed or modified by lake-infilling to restore warmwater fish habitat. We describe how the thermal regimes of these embayments differ from those of small inland lakes, how embayment bathymetry alters the degree of exchange with Lake Ontario, and predict how embayment thermal regimes affect warmwater fish growth. The accumulated growing-degree days, calculated from a 14 °C baseline (∑ GDD₁₄), of seven South-Central Ontario inland lakes and an embayment disconnected from Lake Ontario ranged from 844 to 1157 GDD. Compared to the inland lakes and disconnected embayment, the coastal embayments connected to Lake Ontario achieved fewer ∑ GDD₁₄ and had a greater range, 390-1047, reflecting differences in their degree of exchange with and the cooling effect of Lake Ontario. The thermal regime of coastal embayments differs most from inland lakes during May-late-July. During early summer, mean embayment depth explains over 50% of the variability in ∑ GDD₁₄, with deeper embayments cooling more from lake exchange than shallow embayments. After mid-summer, the cooling embayments are warmed by exchanges with Lake Ontario. This late-summer warming is insufficient to compensate for the cooling effect of the Lake earlier in the summer. Bioenergetic simulations of bluegill, Lepomis macrochirus, growth indicate that most of these embayments are too cool for adequate summer growth of YOY sunfish. Nevertheless, small coastal embayments that are shallow with suitable controls on exchange with the Lake can provide acceptable warmwater fish habitat.     

Development of a submerged aquatic vegetation community index of biotic integrity for use in Lake Ontario coastal wetlands

Submerged aquatic vegetation (SAV) supports biodiversity in the Great Lakes basin by providing an important source of food and habitat for breeding marsh birds and fish and it is desirable to have indices enabling reporting on the condition of SAV, to complement already available indices for the condition of fish, aquatic macroinvertebrate, and bird communities and water quality. We developed a SAV index of biotic integrity (SAV IBI) with 6 years of quadrat-based vegetation species composition data (2003, 2005–2009) collected across 46 coastal wetlands on the Canadian side of Lake Ontario. We evaluated the suitability of thirteen potential metrics that described species richness, floristic quality, and cover. Metrics with a significant linear or non-linear response to disturbance (as assessed by a water quality index; WQI) were retained for use in the SAV IBI. Retained metrics included turbidity-intolerant species richness, native species richness, coefficient of conservatism, and total cumulative coverage. Lower SAV IBI scores indicated poorer coastal wetland conditions. Coastal wetlands in poor condition were located in more urbanized watersheds (e.g., Durham Region) relative to wetlands in more natural watersheds. Fish and breeding bird community condition showed strong significant relationships with the SAV IBI, suggesting that SAV was an important component of fish and bird biodiversity. Our SAV assessment index and its relationship to faunal diversity can be used to inform conservation decisions.     

Origins of Rainbow Smelt in Lake Ontario

The first rainbow smelt (Osmerus mordax) to enter Lake Ontario were probably migrants from an anadromous strain introduced into New York's Finger Lakes. Since the upper Great Lakes were originally stocked with a landlocked strain from Green Lake, Maine, subsequent migration to Lake Ontario from Lake Erie makes Lake Ontario unique among the Great Lakes in probably having received introductions from two distinct populations.     

Wetland vegetation response to record-high Lake Ontario water levels

Lake Ontario water levels were the highest in recorded history in 2017 and 2019, resulting in significant impacts to shoreline properties and observable (but not previously quantified) changes in coastal wetland vegetation. In this study, we assessed differences in coverage of five plant community guilds (submerged aquatic vegetation, Typha, meadow marsh, shrub, and upland) along the shoreline elevation gradient from 12 Lake Ontario coastal wetlands surveyed from 2009 to 2019. This time period included a span of relatively stable water levels (2009–2016), followed by the two high-water years. In general, we found that extreme high water levels led to a decrease in vegetation coverage, most notably at the lower extent of the elevation ranges for the meadow marsh, shrub, and upland vegetation guilds. We also found a modest increase in Typha coverage at the upper extent of its elevation range in 2019, indicating that Typha advanced into the meadow marsh zone during the study period. These findings can be used to calibrate and validate predictive models that inform adaptive management of the new outflow regulation plan for Lake Ontario and can aid in modelling the dynamics of wetland vegetation in relation to predicted changes in Great Lakes water levels due to climate change.     

Dreissena in Lake Ontario 30 years post-invasion

We examined three decades of changes in dreissenid populations in Lake Ontario and predation by round goby (Neogobius melanostomus). Dreissenids (almost exclusively quagga mussels, Dreissena rostriformis bugensis) peaked in 2003, 13 years after arrival, and then declined at depths <90 m but continued to increase deeper through 2018. Lake-wide density also increased from 2008 to 2018 along with average mussel lengths and lake-wide biomass, which reached an all-time high in 2018 (25.2 ± 3.3 g AFTDW/m²). Round goby densities were estimated at 4.2 fish/m² using videography at 10 to 35 m depth range in 2018. This density should impact mussel populations based on feeding rates, as indicated in the literature. While the abundance of 0–5 mm mussels appears to be high in all three years with measured length distributions (2008, 2013, 2018), the abundance of 5 to 12 mm dreissenids, the size range most commonly consumed by round goby, was low except at >90 m depths. Although the size distributions indicate that round goby is affecting mussel recruitment, we did not find a decline in dreissenid density in the nearshore and mid-depth ranges where goby have been abundant since 2005. The lake-wide densities and biomass of quagga mussels have increased over time, due to both the growth of individual mussels in the shallower depths, and a continuing increase in density at >90 m. Thus, the ecological effects of quagga mussels in Lake Ontario are likely to continue into the foreseeable future.     

Low prevalence of VHSV detected in round goby collected in offshore regions of Lake Ontario

Since the first reports of mortalities due to viral hemorrhagic septicemia virus (VHSV) type IVb in the Laurentian Great Lakes basin during 2005 (Lake St. Clair, USA and Bay of Quinte, Lake Ontario, Canada), many groups have conducted surveillance efforts for the virus, primarily in nearshore areas. The round goby (Neogobius melanostomus) has been identified as a key species to target for surveillance, because they have a very high probability of infection at a given site. Our objective in this study was to document and quantify VHSV in round gobies in offshore waters of Lake Ontario using molecular techniques. We collected 139 round gobies from depths ranging from 55 to 150 m using bottom trawls during the early spring of 2011 and detected VHSV in 4 individuals (1/26 fish at 95 m, 2/12 fish at 105 m, and 1/24 fish at 135 m). These results expand the known depth range of VHSV in the Great Lakes. They also have implications on the management of the spread of VHSV within infected bodies of water related to the mixing of populations of fish that would remain distinct in their breeding habitats, but then have the opportunity to mix in their overwintering habitats, as well as to increase overlap of predator and prey species in overwintering habitats.     

Characteristics of nearshore water quality of Lake Ontario coast under Credit Valley Conservation Jurisdiction,Ontario, Canada

The 28.5 km Lake Ontario shoreline along Credit Valley Conservation’s jurisdiction is habitat for native flora and fauna, the source of drinking water for over two million residents, and the location of outfalls for Region of Peel’s two wastewater treatment plants. Some of the significant sources of pollutants to this region are urban tributaries and the Credit River. Instream, shoreside, and nearshore water quality of this region were characterized under this Lake Ontario Integrated Shoreline Strategy study. Eight Parameters of Concern (PoC); water temperature (WT), total suspended solids (TSS), total phosphorous (TP), orthophosphate (OP), nitrate-nitrogen (NO₃-N), Escherichia coli (E. coli), specific conductivity (SC), and pH were studied from 2011 to 2013. Amongst all the PoCs TP was of concern since its instream (75th percentile range: 51.0 µg/L to 188 µg/L), shoreside (75th percentile range: 9.00 µg/L to 53.75 µg/L), and nearshore (75th percentile range: 9.75 µg/L to 19.00 µg/L) concentrations, exceeded their respective objectives of 30 µg/L and 10 µg/L. Other parameters in shoreside/nearshore samples met their respective provincial/federal objectives/guidelines; however, instream E. coli and specific conductivity levels were elevated, reflecting the effects of urbanization. The Lake water temperature moorings recorded lake stratification dynamics, including eight downwelling and five upwelling events during 2011 deployment period. These results provide baseline data for future climate change-related assessment studies.     

Spatiotemporal patterns of water quality in Lake Ontario and their implications for nuisance growth of Cladophora

This study, motivated by a resurgence in Cladophora, investigates changes in the nutrient environment in the littoral zone of Lake Ontario. We measured nutrient concentrations from 2004 to 2008 at two littoral zone (2–12 m) sites on the north shore of Lake Ontario where Cladophora has experienced a resurgence and compared concentrations with data collected in the late 1970s. Spring total phosphorus (TP) and soluble reactive P (SRP) concentrations have significantly declined at these two sites. Furthermore, P loading from the major tributaries to our study sites declined between 1964 and 2008. Upwelling events were not detectably associated with increases in P concentrations at our sites. We conclude that a recent upsurge in nuisance Cladophora, at least at these sites, cannot be explained by deteriorating littoral zone water quality in terms of P concentrations or by changes in catchment loading. For additional context, we also examined trends in coastal (14–20 m) and offshore (> 50 m) nutrients using Environment Canada epilimnetic surveillance data, 1975–2008. Significant declines in TP and SRP concentrations have occurred in north coast waters, concurrent with declines in the offshore. However, nutrient concentrations, notably spring SRP, have not decreased among south coast stations, potentially reflecting greater coastal entrapment of catchment-derived waters. We infer that EC-monitored north coast stations reflect integrated interannual water quality, while south coast stations are more strongly influenced by catchment loading. The effects of higher nutrient concentrations along the south coast, which co-occur with lower water transparency, on benthic algal growth have yet to be determined.     

Effects of Elevated Thermal Regimes on Survival of Rainbow Trout (Salmo Gairdneri) Alevins

Embryos of fall spawning rainbow trout were incubated and alevins reared under thermal regimes characteristic of ambient winter nearshore Lake Ontario and elevated thermal regimes 2 and 5C° warmer than ambient. Embryos incubated under elevated thermal regimes hatched and attained 50% swim-up sooner than embryos incubated under the ambient thermal regime. In general, mortality of alevins at 21 and 28 days after swim-up was low for all rearing thermal regimes. The generally low mortality of alevins incubated and reared under the various thermal regimes suggests that rainbow trout alevins have fairly broad thermal tolerances when food is provided to excess.     

Nutrient footprints on the Toronto-Mississauga waterfront of Lake Ontario

The extent of nutrient enrichment over the urbanized shoreline of western Lake Ontario bordering the Cities of Toronto and Mississauga was investigated in 2018. Concentrations of total phosphorus were higher and more wide-ranging compared with nearshore reference areas in eastern Lake Ontario. Area-weighted chlorophyll a was higher over the shoreline from the mouth of the Credit River to Humber Bay west of Toronto Harbour compared with that to the east from the Toronto Beaches to the Rouge River, a pattern also seen broadly in concentrations of phosphorus fractions and nitrates. Concentrations of phosphate measured by mass spectrometry, and using an internal standard to minimize sampling losses, were higher in Toronto Inner Harbour, near wastewater outfalls, river mouths, and to varying extent over the mixing areas of these discharges. Chlorophyll a suggested broadly oligotrophic to oligo-mesotrophic conditions despite areas with nutrient fractions suggestive of more productive conditions. Toronto Inner Harbour was mesotrophic, with wide-ranging levels of phosphorus fractions strongly influenced by the variable loading from the Don River into the harbour. Phosphorus fractions in the harbour quays which also receive CSOs discharges were elevated at times. Blooms or scums of planktonic algae were not observed. Elevated concentrations of phosphate were found at shallow depths suitable for growth of the green algae Cladophora. As these urban areas continue to grow, the potential for additional nutrient loading to exacerbate growth of algae should be watched given the present conditions that indicate variable but pervasive nutrient enrichment.     

Habitat use by subyearling Chinook and coho salmon in Lake Ontario tributaries

The habitat use of subyearling Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) was examined in three tributaries of Lake Ontario. A total of 1781 habitat observations were made on Chinook salmon (698) and coho salmon (1083). During both spring and fall, subyearling coho salmon used pool habitat with abundant cover. During spring, principal component analysis revealed that water depth was the most important variable governing subyearling Chinook salmon habitat use. Substrate materials used by Chinook salmon in the spring and coho salmon in the fall were significantly smaller than were present on average within the study reaches. When the two species occurred sympatrically during spring they exhibited similar habitat selection. Although the habitat used by coho salmon in Lake Ontario tributaries was consistent with observations of habitat use in their native range, higher water velocities were less important to Chinook salmon than has previously been reported.     

Egg Thiamine Status of Lake Ontario Salmonines 1995–2004 with Emphasis on Lake Trout

Alewives (Alosa pseudoharengus), the major prey fish for Lake Ontario, contain thiaminase. They are associated with development of a thiamine deficiency in salmonines which greatly increases the potential for developing an early mortality syndrome (EMS). To assess the possible effects of thiamine deficiency on salmonine reproduction we measured egg thiamine concentrations for five species of Lake Ontario salmonines. From this we estimated the proportion of families susceptible to EMS based on whether they were below the ED20, the egg thiamine concentration associated with 20% mortality due to EMS. The ED20s were 1.52, 2.63, and 2.99 nmol/g egg for Chinook salmon (Oncorhynchus tshawytscha), lake trout (Salvelinus namaycush), and coho salmon (Oncorhynchus kisutch), respectively. Based on the proportion of fish having egg thiamine concentrations falling below the ED20, the risk of developing EMS in Lake Ontario was highest for lake trout, followed by coho (O. kisutch), and Chinook salmon, with the least risk for rainbow trout (O. mykiss). For lake trout from western Lake Ontario, mean egg thiamine concentration showed significant annual variability during 1994 to 2003, when the proportion of lake trout at risk of developing EMS based on ED20 ranged between 77 and 100%. Variation in the annual mean egg thiamine concentration for western Lake Ontario lake trout was positively related (p < 0.001, r² = 0.94) with indices of annual adult alewife biomass. While suggesting the possible involvement of density-dependent changes in alewives, the changes are small relative to egg thiamine concentrations when alewife are not part of the diet and are of insufficient magnitude to allow for natural reproduction by lake trout.     

Great Lakes coastal fish habitat classification and assessment

Basin-scale assessment of fish habitat in Great Lakes coastal ecosystems would increase our ability to prioritize fish habitat management and restoration actions. As a first step in this direction, we identified key habitat factors associated with highest probability of occurrence for several societally and ecologically important coastal fish species as well as community metrics, using data from the Great Lakes Aquatic Habitat Framework (GLAHF), Great Lakes Environmental Indicators (GLEI) and Coastal Wetland Monitoring Program (CWMP). Secondly, we assessed whether species-specific habitat was threatened by watershed-level anthropogenic stressors. In the southern Great Lakes, key habitat factors for determining presence/absence of several species of coastal fish were chlorophyll concentrations, turbidity, and wave height, whereas in the northern ecoprovince temperature was the major habitat driver for most of the species modeled. Habitat factors best explaining fish richness and diversity were bottom slope and chlorophyll a. These models could likely be further improved with addition of high-resolution submerged macrophyte complexity data which are currently unavailable at the basin-wide scale. Proportion of invasive species was correlated primarily with increasing maximum observed inorganic turbidity and chlorophyll a. We also demonstrate that preferred habitat for several coastal species and high-diversity areas overlap with areas of high watershed stress. Great Lakes coastal wetland fish are a large contributor to ecosystem services as well as commercial and recreational fishery harvest, and scalable basin-wide habitat models developed in this study may be useful for informing management actions targeting specific species or overall coastal fish biodiversity.     

Heatwaves and storms contribute to degraded water quality conditions in the nearshore of Lake Ontario

As extreme climatic events, such as heatwaves and storms, become more frequent in response to changing climates, understanding the role climatic events play on water quality is essential. Here, we use water quality monitoring data collected from the nearshore of Lake Ontario between 2000 and 2018 to ask: i) which sites in the nearshore of Lake Ontario have statistically extreme water quality conditions?; ii) do water quality conditions differ in extreme versus non-extreme climate years?; and iii) what are the significant antecedent extreme weather drivers of water quality in the nearshore of Lake Ontario? Three sites with the highest chlorophyll a concentrations and eutrophic conditions, two of which are in Areas of Concern, exhibited the strongest responses to climate extremes. Antecedent weather conditions explained 87.2% of the variation in extreme chlorophyll a concentrations. In particular, warmer temperatures and heatwaves corresponded with statistical extremes in chlorophyll a concentrations. Precipitation accounted for 35.5% of the variation in extreme conditions of turbidity, including storm events the day prior to sampling. When considering site-specific extreme conditions, antecedent weather conditions explained 66.8% of the variation in turbidity. We illustrate the strong role that heatwaves and storm events play on spatial and temporal patterns in extreme water quality conditions, highlighting the importance of incorporating climate change adaptation plans into ecosystem management strategies to preserve water quality in the highly important and iconic nearshore regions of the Laurentian Great Lakes.     

Seasonal Food of Juvenile Lake Trout in U.S. Waters of Lake Ontario

Stomach contents of 3,554 lake trout (Salvelinus namaycush), 100 to 449 mm in total length, captured with bottom trawls during April through October 1978–81 along the south shore of Lake Ontario were examined. Invertebrates appeared to be an important food of lake trout less than 200 mm long but were only occasionally eaten by larger fish. For all seasons and size groups of juvenile lake trout combined, the slimy sculpin (Cottus cognatus) was the principal forage fish, making up 42% (by weight) of identifiable fish remains. Young-of-the-year slimy sculpins were a major food of recently stocked yearling lake trout during July through October. Alewives (Alosa pseudoharengus) were the principal forage during April and May, and made up 28% (by weight) of the identifiable fish remains. They were rarely eaten during July and August, however, when lake trout remained in the hypolimnion and alewives were above it. Over 99% of the alewives eaten from April through August were yearlings and over 99% eaten during October were young-of-the-year. Rainbow smelt (Osmerus mordax) were the primary forage during July and August, but contributed only a small part of the diet during other seasons; overall, they made up 25% of identifiable fish remains. Johnny darters (Etheostoma nigrum) made up 4% of identifiable fish remains and were most common in stomachs of small lake trout during October.     

Initial insights on the thermal ecology of lake whitefish in northwestern Lake Michigan

Lake whitefish Coregonus clupeaformis are a native coldwater species supporting important recreational and commercial fisheries in the Laurentian Great Lakes. Climate-related changes in water temperature may have important implications for the future sustainability of these fisheries. However, projecting future habitat availability is difficult because limited information is available on lake whitefish thermal ecology in the region. In this study, archival temperature loggers were implanted into 400 lake whitefish from northwestern Lake Michigan, including Green Bay, during October–November 2017. Loggers recorded temperature for 11 months at 4-hr intervals. Thirteen recovered temperature loggers were used in analyses. In winter (1 December–31 March), temperatures occupied by lake whitefish ranged from 0 to 8.0 °C, while in spring (1 April–31 May) temperatures ranged from 0 to 20.0 °C. In summer (1 June–15 September) and fall (16 September–7 November), lake whitefish occupied temperatures of 4–21.5 and 4–21.0 °C, respectively. Average temperatures in summer (10.8 °C) were within the previously proposed optimal temperature range (10–14 °C) and broad thermal niche (7–17 °C); however, 58% of observations were outside the optimal temperature range and 11% of observations were outside the broad thermal niche. Our results suggest that lake whitefish from northwestern Lake Michigan inhabit temperatures both above and below previously reported expected temperature ranges. This study provides initial insights on lake whitefish thermal ecology in Lake Michigan and can be used as a baseline for future work aimed at determining how lake whitefish habitat availability may change in the future.     

Six decades of Lake Ontario ecological history according to benthos

The Laurentian Great Lakes have experienced multiple anthropogenic changes in the past century, including cultural eutrophication, phosphorus abatement initiatives, and the introduction of invasive species. Lake Ontario, the most downstream lake in the system, is considered to be among the most impaired. The benthos of Lake Ontario has been studied intensively in the last six decades and can provide insights into the impact of environmental changes over time. We used multivariate community analyses to examine temporal changes in community composition over the last 54 years and to assess the major drivers of long-term changes in benthos. The benthic community of Lake Ontario underwent significant transformations that correspond with three major periods. The first period, termed the pre/early Dreissena period (1964–1990), was characterized by high densities of Diporeia, Sphaeriidae, and Tubificidae. During the next period defined by zebra mussel dominance (the 1990s) the same groups were still prevalent, but at altered densities. In the most recent period (2000s to present), which is characterized by the dominance and proliferation of quagga mussels deeper into the lake, the community has changed dramatically: Diporeia almost completely disappeared, Sphaeriidae have greatly declined, and densities of quagga mussels, Oligochaeta and Chironomidae have increased. The introduction of invasive dreissenids has changed the Lake Ontario benthic community, historically dominated by Diporeia, Oligochaeta and Sphaeriidae, to a community dominated by quagga mussels and Oligochaeta. Dreissenids, especially the quagga mussel, were the major drivers of these changes over the last half century.     

Habitat use and diet composition of juvenile Atlantic salmon in a tributary of Lake Ontario

The habitat use and diet of juvenile Atlantic salmon Salmo salar was examined in the South Sandy Creek drainage that discharges into eastern Lake Ontario. Subyearling salmon were stocked in early May during two consecutive years, and habitat and diet evaluations were made in mid-July and mid-October in 2005 and 2006. Both subyearling and yearling Atlantic salmon occupied deeper and faster areas that had more cover and larger sized substrate materials than was present, on average, within the study reach. Differences in habitat use between subyearling and yearling salmon only occurred in summer. Principal component analysis showed that of the habitat variables examined, the amount of cover and size of substrate were more important to juvenile salmon in summer, whereas depth and velocity were more important in the fall. Trichopteran larvae (mainly hydropsychids) dominated the diet of juvenile Atlantic salmon, and parr were feeding most heavily from the substrate as compared to the drift. The juvenile ecology of this re-introduced population of Atlantic salmon is consistent with that reported in other studies throughout the species native range.     

Circulation and mixing in Sodus Bay due to water exchange with Lake Ontario

Embayments on large lakes may be affected by water exchange with the lake that, in turn, impact water quality in the embayment. In this study we examine the influence of hydrodynamic factors that may play a role in controlling water quality in Sodus Bay, the largest enclosed embayment on the U.S. shoreline of Lake Ontario. The motivation for this study was the occurrence of a blue-green algal (cyanobacterial) bloom in 2010, and the need to understand the factors that influence this and other water quality issues. A hydrodynamic model with high spatial and temporal resolution was applied and calibrated to field data collected in a detailed sampling program in 2013. The model, along with field data collected over several additional years, was then used to develop a comprehensive understanding of the hydrodynamic impacts on physical conditions in the bay. A primary result of this process is a determination of the importance of flow exchange between Lake Ontario and Sodus Bay, particularly during lake upwelling periods that cause colder water to enter the bay as an underflow. Hydrodynamic features identified to have played a potential role in the bloom formation of 2010 include a lake upwelling event, strong stratification, and relatively warm conditions throughout much of the summer. Lack of continuous monitoring in 2010 precludes a specific comparison of the model and data when the bloom formed, but the model clearly shows conditions that would have led to a bloom, assuming other preconditions were in place. The customized hydrodynamic model provides opportunities for future ecological modeling, hypothesis development, and what-if scenario testing. This study reinforces the importance of hydrodynamic interactions between lakes and embayments, and their impacts on water quality.