Onondaga Lake, located near Syracuse, New York, was once infamous for being one of the most contaminated bodies of water in the United States. For over a century, industrial discharge and municipal waste severely degraded the lake’s ecosystem, leading to environmental and public health crises. The lake’s notoriety as an environmental disaster became a defining characteristic of the region, ultimately leading to its designation as a federal Superfund site. Massive, multi-decade efforts have since been launched to reverse the damage, transforming the lake’s environmental status. The question today is how successful those efforts have been and whether the lake is truly safe for public use.
Legacy of Contamination
The lake’s severe pollution began in the late 19th century with the establishment of the Solvay Process Company on its southwestern shore. This company produced soda ash, discharging millions of tons of waste by-products, primarily composed of calcium, sodium, and chloride, directly into the lake and surrounding wetlands. This industrial activity drastically altered the lake’s natural chemistry and physical environment, creating large wastebeds along the shoreline.
The contamination intensified with the introduction of mercury cell chlorine production in 1946 by Allied Chemical. Between 1946 and 1970, an estimated 165,000 pounds of mercury were discharged into the lake, poisoning the water and saturating the sediments. Onondaga Lake was added to the federal Superfund National Priorities List in 1994 due to the volume and toxicity of this waste. Primary contaminants included mercury, polychlorinated biphenyls (PCBs), and chlorinated benzenes, which persisted in the lake bottom and surrounding upland areas.
The Massive Cleanup Effort
The comprehensive revitalization of Onondaga Lake involved complex, large-scale engineering and regulatory initiatives. One of the largest components addressed the contaminated lake bottom through sediment removal and isolation. Over 2.2 million cubic yards of highly contaminated sediment were hydraulically dredged, removing the most concentrated “hot spots” of mercury and other chemicals.
Following dredging, capping was implemented to isolate remaining contaminants. This involved placing layers of clean materials—including sand, stone, and activated carbon—over approximately 475 acres of the lake bottom. The cap acts as a physical and chemical barrier, preventing buried toxic sediments from mixing with the water column. Reactive core capping was used in some areas to chemically stabilize and contain contaminants like mercury.
A second major initiative focused on controlling pollutant inputs from the surrounding watershed, particularly those related to municipal waste. Upgrades to the Metropolitan Syracuse Wastewater Treatment Plant (Metro) significantly reduced the discharge of nutrients like phosphorus and ammonia into the lake. Furthermore, a substantial program was implemented to mitigate Combined Sewer Overflows (CSOs), which historically released untreated sewage and pathogens into the lake during heavy rainfall, dramatically reducing the volume of these overflows.
Habitat restoration efforts completed the cleanup plan, focusing on creating and enhancing wetlands and near-shore areas. These areas are designed to provide sustainable ecosystems and act as natural filters for tributary inputs.
Measuring Current Water Quality
Scientific monitoring confirms the cleanup has led to dramatic improvements in the lake’s overall environmental health. Reductions in nutrient loading have been particularly successful; the lake shifted from a hypereutrophic (highly nutrient-rich) state to a mesotrophic (moderately productive) state. Upgrades to the Metro plant reduced total phosphorus discharge by approximately 86% and eliminated ammonia releases, leading to the lake’s removal from the state’s impaired water list for ammonia.
Water clarity has also improved significantly, with Secchi disk readings showing greater transparency, which encourages the growth of native aquatic plants. A targeted effort to reduce mercury bioaccumulation involved adding calcium nitrate to the deep-water sediments. This treatment inhibits the production of methylmercury—the form most easily absorbed by organisms—leading to a dramatic reduction in methylmercury concentrations in the water column.
These improvements have resulted in a notable ecological recovery, with the lake now supporting a much more diverse aquatic community. The number of fish species documented in the lake has increased substantially, now exceeding 65 different types, including the return of sensitive species like brown trout. This improved biodiversity serves as a strong ecological indicator that the lake’s water quality and habitat structure are the cleanest they have been in over a century.
Practical Implications for Recreation and Health
The scientific recovery of Onondaga Lake translates into expanded recreational opportunities for the public, although certain restrictions remain due to the lake’s environmental legacy. The historical ban on swimming, initially imposed in 1940 due to bacterial contamination from sewage, was lifted in 2015 following the major reductions in municipal waste and CSOs. Today, the lake is considered safe for contact recreation, and new swimming areas have been developed or are planned.
However, the persistent nature of contaminants in the sediment dictates continued caution regarding fish consumption. The New York State Department of Health (DOH) maintains strict fish consumption advisories for Onondaga Lake due to the bioaccumulation of mercury and PCBs in the food chain. The DOH advises children under the age of 15 and women under the age of 50 to eat no fish caught from the lake. For the general population, consumption is severely limited; for instance, no walleye, carp, channel catfish, or white perch should be eaten. These advisories underscore that while water quality has dramatically improved, the legacy of industrial pollution remains, necessitating continued monitoring and public awareness.