On June 20, the Onondaga Nation invited all to a peaceful gathering to honor the lake, formerly one of the most polluted in the country. In 1994, the Environmental Protection Agency listed Lako Onondaga as a superfund site consisting of lake itself, seven major and minor tributaries, and upland sources of contamination to the site (called subsites), of which there are eleven.
Because of the presence of salt and limestone, Onondaga Lake was a prime location for the Solvay Process Company to set up its operations. Solvay was later absorbed by Allied Chemical, and is now known as Honeywell International, Inc. Starting in 1946, Allied Chemical used a mercury cell process that released waste streams containing mercury and heavy metals into the lake.
Discharge of chemical waste into the lake left it teeming with chemicals—the EPA profile explains that "surface water is contaminated with mercury, and sediments are contaminated with polychlorinated biphenyls (PCBs); pesticides; creosotes; heavy metals including lead, cobalt, and mercury; polycyclic aromatic hydrocarbons (PAHs); and volatile organic compounds (VOCs) such as chlorobenzene."
Due to efforts by the EPA and the New York Department of Environmental Conservation, the condition of Onondaga Lake has improved remarkably. Quantities of phosphorus, ammonia, and other major pollutants in the lake have decreased substantially. Fisheries have recovered faster than expected, and the lake is now home to 56 species of fish—up from an estimated 9 to 12 species in the 1970s.