Lake Superior’s forested watershed and coastal wetlands help maintain water quality and a healthy aquatic ecosystem.
Lake Superior continues to be a good source of high-quality drinking water. Most toxic chemicals monitored in Lake Superior are low compared to other Great Lakes and long-term trends indicate that concentrations are declining. Lake Superior fish continue to be a nutritious food source and contaminant concentrations in fish filets are currently stable. However, fish consumption advisories continue to be in effect for some species.
Overall, beaches and nearshore waters in Lake Superior are clear and clean and provide good opportunities for swimming and recreational use, with only occasional closures or advisories. Naturally lower water temperatures promote resilience to nutrient and bacterial pollution and current nutrient levels remain similar to historic values. However, impacts of climate change include increasing lake water temperatures which may threaten this natural resiliency. Some short-lived, non-toxic blooms of cyanobacteria occur primarily in the area between Duluth Harbor and the Apostle Islands.
Overall, Lake Superior has the best habitat and species conditions of all the Great Lakes. Overall, coastal wetlands in the Lake Superior basin are in Fair condition. While 62% of surveyed wetland sites have plant communities that are assessed as Good, there are numerous wetlands that are degraded. The health of the lake is dependent on the health of the watersheds and the tributaries that connect them. Lack of habitat connectivity has affected some native fish species such as Lake Sturgeon, but conditions are Improving. Lake Trout are in Good condition, supported by a stable and diverse prey fish population. The lower food web is healthy with the small shrimp-like species of Diporeia at Good levels. The Lake Superior prey fish community is dominated by native species, a condition not found in other Great Lakes. Invasive species, particularly Sea Lamprey, are still causing harm to predatory fish such as Lake Trout. Adult Sea Lamprey populations are above target levels.
Groundwater quality is assessed as Good based on nitrate and chloride, however there are limited data in northern parts of the basin. The Lake Superior basin has a high percentage of natural land cover, which is at low risk of habitat and water quality degradation. Still, the lake is experiencing changes such as warming waters and decreasing ice cover due to long-term climate shifts.