Lake Ontario shows improvements with fewer beach closings and declines in contaminant concentrations in fish.
Lake Ontario continues to be a good source of high-quality drinking water. Toxic chemicals monitored in Lake Ontario are assessed as Fair and long-term trends indicate that concentrations are declining, including declines in contaminant concentrations in fish filets. Lake Ontario fish continue to be a nutritious food source. While consumption advisories for certain species of fish remain in effect, some have recently become less restrictive due to several decades of clean-up efforts.
Lake Ontario beaches and nearshore waters provide good opportunities for swimming and other recreational use. Over the past 10 years, the percentage of days during the swimming season that Lake Ontario monitored beaches are open and safe for swimming has increased. Excessive growth of Cladophora is problematic in some nearshore areas due in part to nutrient loading and increased water clarity caused by the filtering effects of invasive mussels. The current status of harmful algal blooms in Lake Ontario is Good with an Unchanging trend, although there are localized impaired zones in some embayments. Nutrient concentrations are considered to be Fair due to offshore phosphorus levels that are below objectives. Further work is underway to ascertain the impact of current phosphorus concentrations on offshore lake productivity, including impacts on fish populations.
Coastal wetlands have been impacted by development, past water level regulation and invasive species such as Phragmites and Hybrid Cattail, however, coastal wetland amphibians and birds are showing Improving trends. Habitat connectivity between the tributaries and the lake is Fair and the trend is Improving. Lake Trout populations are improving, due in part to successful Sea Lamprey control. Prey fish are in Fair condition; some native prey fish, such as Deepwater Sculpin, are recovering naturally and restoration efforts for populations of other native prey fish are proving successful. Lake Sturgeon populations are showing some signs of recovery with spawning occurring in a few tributaries. Phytoplankton and zooplankton communities are assessed as Good. However, Diporeia, an important food source for prey fish, is now rarely found during regular sampling. Invasive species, including Sea Lamprey, invasive mussels and Phragmites, have significantly altered habitat and the food web in Lake Ontario.
Groundwater quality is assessed as Fair with elevated chloride levels due to road salt being an issue. Land-based stressors continue to impact Lake Ontario including the rapid urban population growth in the western part of the Canadian side of the basin. Human population in the Lake Ontario basin has increased by more than 60% over the past 50 years which is the highest of all the Great Lakes basins. Shifts in climate trends such as increasing surface water temperatures and decreasing ice cover may have ecosystem implications.