A Historical Review of Water Quality Conditions in Lake Erie Watershed from 1928 to 2022

Lake Erie is the smallest and shallowest of the Great Lakes, and approximately 12 million people live in the watershed that includes 17 metropolitan areas. Lake Erie is the significant resource for drinking water; during the 1960s water quality issues became a concern, and Lake Erie was perceived to be “dying.” By the late 1960s, Canadian and American regulatory agencies agreed that limiting phosphorus loads was the key to controlling excessive algal growth and that a coordinated lake wide approach was necessary. This resulted in open lake phosphorus concentrations declined, by more than 62% of the total phosphorus load during 1968–1981; these decreases were attributed to the phosphorus abatement program on municipal sources, restriction of phosphate concentrations in detergents, and no-till farming. However, since 2003, in-lake concentrations of soluble reactive phosphorus and overall phytoplankton biomass (often dominated by the HAB genus Microcystis) have increased, while annual total phosphorus loading to the lake has remained below the 11-kilotonne level as mandated. Agricultural nonpoint sources of soluble reactive phosphorus have increased and contribute a larger proportion of total phosphorus loads to the Lake Erie. Further, nitrogen has been identified as potentially capable of limiting growth of freshwater cyanobacterial blooms, and it is suggested nitrogen loads to the lake should be controlled. Currently, the governors of Ohio and Michigan and the premier of Ontario committed to reducing phosphorus loadings to Lake Erie by 40%. This history of nutrient discharge to the Lake Erie and regulatory requirements are elucidated in the paper.