Onondaga Lake

Onondaga Lake is a lake in Central New York, immediately northwest of and adjacent to Syracuse, New York. The southeastern end of the lake and the southwestern shore abut industrial areas and expressways; the northeastern shore and northwestern end border a series of parks and museums.

Although it is near the Finger Lakes region, it is not traditionally counted as one of the Finger Lakes. Onondaga Lake is a dimictic lake, meaning that the lake water completely mixes from top to bottom twice a year. The lake is 4.6 miles long and 1 mile wide making a surface area of 4.6 square miles. The maximum depth of the lake is 63 feet with an average depth of 35 feet. Its drainage basin has a surface area of 642 square kilometers, encompassing Syracuse, Onondaga County except the eastern and northern edges, the southeastern corner of Cayuga County and the Onondaga Nation Territory, and supports approximately 450,000 people.

Onondaga Lake has two natural tributaries that contribute approximately 70% of the total water flow to the lake. These tributaries are: Ninemile Creek and Onondaga Creek. The Metropolitan Syracuse Wastewater Treatment Plant (METRO) contributes 20% of the annual flow. No other lake in the United States receives as much of its inflow as treated wastewater. The other tributaries, which include Ley Creek, Seneca River, Harbor Brook, Sawmill Creek, Tributary 5A, and East Flume, contribute the remaining 10% of water flow into the lake. The tributaries flush the lake out about four times a year. Onondaga Lake is flushed much more rapidly than most other lakes. The lake flows to the northwest and discharges into Seneca River which combines with the Oneida River to form the Oswego River, and ultimately ends up in Lake Ontario.

The lake is considered sacred within the indigenous territory of the Onondaga Nation. The Onondaga people had control of the lake taken from them by New York state following the American Revolutionary War. During the late 19th century, European-Americans built many resorts along the lake's shoreline, as it was a destination of great beauty. The Onondaga Nation continues to have a religious and cultural presence on the shores of the lake, today.

With the industrialization of the region, much of the lake's shoreline was developed; domestic and industrial waste, due to industry and urbanization, led to the severe degradation of the lake. Unsafe levels of pollution led to the banning of ice harvesting as early as 1901. In 1940, swimming was banned, and in 1970 fishing was banned due to mercury contamination. Mercury pollution is still a problem for the lake today. Despite the passage of the Clean Water Act in 1973 and the closing of the major industrial polluter in 1986, Onondaga Lake remained one of the most polluted lakes in the United States until several initiatives, including a 15-year multi-stage program completed in late 2017, allowed the lake to reach criteria required by the New York State Department of Environmental Conservation and the United States Environmental Protection Agency. This includes implementing a long-term operation, maintenance, and monitoring program to ensure the effectiveness of the remedy.