Along the Toronto shoreline, small coastal embayments (0.4 – 32 ha) are being constructed or modified to restore warmwater fish habitat. I describe how Lake Ontario (hereafter the Lake) alters the thermal regime of these small coastal embayments, how the altered thermal regimes affect growth and survival of age-0 warmwater fishes, and how the thermal habitat quality for such fishes can be improved by altering embayment design. During the warming period of the ice-free season, embayments warm faster than the Lake and so are cooled by exchanges with the Lake. Later in the year Lake exchange warms the rapidly cooling embayments, but the net effect of Lake-embayment exchange is cooling. The degree of cooling in Toronto’s small coastal embayments varies; many have temperatures near that of the Lake, and a few warm as much as local ponds. Age-0 pumpkinseed (Lepomis gibbosus) can fail to reach sufficient size to survive the winter in cooler embayments because their spawning is delayed and their growth is slowed. Most embayments along the Toronto shoreline are too cold to produce age-0 fish that can survive the winter, but all embayments are occupied by age >1 pumpkinseed, suggesting movement from warmer to cooler embayments. Using otolith microchemistry to identify natal embayments of fish, I confirm that age-0 and age-1 pumpkinseed, as well as age-0 largemouth bass (Micropterus salmoides) and age-0 yellow perch (Perca flavescens), exist in metapopulations. Embayment bathymetry is a poor predictor of temperature because almost all embayment flushing rates are very fast, usually 1-2 days. Warmer embayments are located in protected areas of Lake Ontario and receive waters that have already heated substantially. Cold embayments are located along the exposed shoreline of Lake Ontario. To protect embayments from cold lake waters, the cross-sectional area of embayment channels need to be reduced to 1-10% of their current size.

Along the Toronto shoreline, small coastal embayments (0.4 – 32 ha) are being constructed or modified to restore warmwater fish habitat. I describe how Lake Ontario (hereafter the Lake) alters the thermal regime of these small coastal embayments, how the altered thermal regimes affect growth and survival of age-0 warmwater fishes, and how the thermal habitat quality for such fishes can be improved by altering embayment design. During the warming period of the ice-free season, embayments warm faster than the Lake and so are cooled by exchanges with the Lake. Later in the year Lake exchange warms the rapidly cooling embayments, but the net effect of Lake-embayment exchange is cooling. The degree of cooling in Toronto’s small coastal embayments varies; many have temperatures near that of the Lake, and a few warm as much as local ponds. Age-0 pumpkinseed (Lepomis gibbosus) can fail to reach sufficient size to survive the winter in cooler embayments because their spawning is delayed and their growth is slowed. Most embayments along the Toronto shoreline are too cold to produce age-0 fish that can survive the winter, but all embayments are occupied by age >1 pumpkinseed, suggesting movement from warmer to cooler embayments. Using otolith microchemistry to identify natal embayments of fish, I confirm that age-0 and age-1 pumpkinseed, as well as age-0 largemouth bass (Micropterus salmoides) and age-0 yellow perch (Perca flavescens), exist in metapopulations. Embayment bathymetry is a poor predictor of temperature because almost all embayment flushing rates are very fast, usually 1-2 days. Warmer embayments are located in protected areas of Lake Ontario and receive waters that have already heated substantially. Cold embayments are located along the exposed shoreline of Lake Ontario. To protect embayments from cold lake waters, the cross-sectional area of embayment channels need to be reduced to 1-10% of their current size.

To simplify water quality improvement in reservoirs, it has been suggested that efforts should be focused on smaller and more manageable units such as reservoir embayment areas. Embayments are prime locations to locate marinas, parks, beaches, and residential homes. Current data and information on reservoir embayments in Tennessee was assembled into a GIS-based database. Embayments of 11 main reservoirs were mapped and digitized in ArcGIS. Initial characterization criteria include watershed size, embayment area-watershed ratio, maximum residence time, and stream influence on embayments. The characterization process was then applied to the mapped reservoir embayments in Tennessee to identify and prioritize embayments that are most likely to be affected by watershed restoration efforts. This process has potential to used by resource agencies and stakeholders to prioritize water quality improvements in reservoir embayments.