A clean lake reflects well on all of us.


Pollutants & Onondaga Lake


Phosphorus is an element that is important to plant nutrition. It is commonly found in high concentrations in fertilizers and sewage. The amount of phosphorus received by a lake is an important factor in determining water quality because phosphorus promotes the growth of algae. Algae are microscopic green plants that live in lakes.

Phosphorus Load Sources

Phosphorus loads fall into two categories: point and nonpoint sources. Treated domestic and industrial wastes discharged from a pipe into Onondaga Lake represent a point source input.

Some of phosphorus enters the tributaries from nonpoint sources such as runoff carried from the land. Other sources of phosphorus to the tributaries are from combined sewer overflows (CSOs) which discharge untreated sewage and stormwater to Onondaga Creek, Ley Creek, and Harbor Brook.

Algae Blooms

Phosphorus loading causes excess growth of algae (referred to as algae blooms) in Onondaga Lake throughout most of the summer. The algae give the water a cloudy green appearance and decrease the Lake's water clarity.

Most of the algae produced in the upper layers of Onondaga Lake ultimately settle to the bottom where they are decomposed by bacteria and fungi. Oxygen is used in the decomposition process. The greater the algae production in the upper layers, the greater the loss of dissolved oxygen from the lower layers of the lake.

Water Clarity

One way to see the effects of phosphorus pollution in Onondaga Lake is to measure the lake's water clarity. Scientists routinely measure the clarity of Onondaga Lake by recording the depth at which a black and white Secchi disk can no longer be seen when lowered into the water.

The NYS Health Department standard for opening a beach on Onondaga Lake requires that the lake's clarity be 4 feet or greater throughout the summer. This is a matter of public safety so that people can be seen in the water. From 1970 to 1986 the lake's water clarity exceeded 4 feet only 1 day of 5.

Ammonia & Nitrite

Ammonia and nitrite are forms of nitrogen that, in high concentrations, can be toxic to fish and other aquatic life. Ammonia and nitrite standards (regulations) were developed to prevent fish kills and to protect fish spawning and free migration. The effect of ammonia on water quality depends on a complex relationship among the amount of ammonia, pH, and the temperature of the water. Chronic exposure to elevated ammonia levels can reduce natural fish spawning and restrict migration patterns.

Bacteria, debris 

Some areas of Syracuse have sewers that carry both sanitary sewage—from homes and businesses—and also stormwater from the streets. During dry weather these sewers carry all the sanitary sewage to the Metropolitan Syracuse Wastewater Treatment Plant for treatment.

During times of heavy rain or melting snow, however, the amount of water is greater than the capacity of the sewers. At these times, the sewers overflow and discharge the excess—a combination of runoff and sanitary sewage—into Onondaga Creek and Harbor Brook. This wastewater—combined sewer overflow (CSO)—eventually gets to Onondaga Lake. The sewer system was designed to overflow in this way to prevent sewage from backing up into streets and basements.

CSOs create human health risks because they add bacteria, floating trash, organic material, heavy solids, and grit to city streams and Onondaga Lake. Material from CSOs collects on vegetation along and in streams. It looks bad and smells bad, and it can also transmit disease to humans who may come in contract with the water. Material from CSOs also depletes the dissolved oxygen in the water that is necessary for aquatic life..

Mercury & Other Industrial Chemicals 

Mercury is a metal that is found in a variety of forms. Methyl mercury, formed in aquatic systems through the activity of certain bacteria, is among the most poisonous chemicals known. If all the mercury in the average fever thermometer were converted to methyl mercury, it would be enough to render more than 10,000 1-pound largemouth bass unfit for human consumption. Mercury has been measured in the flesh of fish taken from Onondaga Lake.

Mercury Sources

The Honeywell chlor-alkali facility discharged an estimated 165,000 pounds of mercury to Onondaga Lake from 1946 until 1970 under operation by Allied Chemical. Mercury loading to the Lake was greatly reduced between 1970 and 1988. As a result, the lake bottom sediments are listed as a hazardous waste site.

The exact source of mercury to the fish in Onondaga Lake is being studied. Scientists are currently investigating the lake's tributaries and sediments to identify why Onondaga Lake fish are still being contaminated.

Honeywell is implementing remediation under the direction of NYS to limit major sources of mercury to the lake system and eliminate contamination of the fish.

Other Toxic Substances

PCBs, and chlorinated benzenes, and other toxic substances have also been detected in the Lake ecosystem. Mercury, however, remains the contaminant of most concern because of its persistence in the fish.

Sediment Loading: Tully Valley Mudboils 

Mudboils are holes in the earth that discharge mud and soft sediments from underground. They are associated with groundwater flow under pressure. The Tully Valley mudboils are located about 15 miles upstream from the mouth of Onondaga Creek in southern Onondaga County.

Tully Valley mudboil

Newspapers reported mudboils in Tully as early as 1899. Anecdotal information indicates the amount of sediments that they have discharged to Onondaga Creek has increased over the years.

The occurrence of the mudboils have been attributed to Allied-Signal's solution mining activities in the Tully Valley, although there is disagreement over this contention. According to the U.S. Geological Survey, the average sediment loading to Onondaga Creek from the mudboil area between October 1991 and March 1992 was approximately 30 tons per day.

Sedimentation Effects on Onondaga Creek and Lake

Onondaga Creek has a murky muddy-brown appearance especially during high water as a result of high concentrations of clay and silt in the Creek. Most of these materials come from the Tully Valley mudboils. Much of the stream bed below from the mudboil area is covered with sediments discharged from the mudboils. The muddy sediments:

Onondaga Creek contributes more than 50% of the annual tributary sediment load to the lake due in large part to the mudboils.

Mudboil Remediation Efforts

Since 1992, the Onondaga Lake Partnership (and formerly, the Onondaga Lake Management Conference) has supported, through the efforts of he United States Geologic Survey (USGS), the following remedial activities:

These efforts have been successful in reducing the amount of sediment flowing into the Onondaga Creek, to less than 1 ton/day.

Other Sedimentation Sources

High concentrations of calcium discharged to the lake from soda ash production caused massive quantities of calcium carbonate to accumulate on the lake bottom. These deposits have accelerated the rate at which Onondaga Lake is filling in and eliminated habitats suitable to support a normal near-shore biological community.


The concentration of dissolved salts in water is referred to as salinity. The water in the oceans, which is about 3.5% salt by its weight, is extremely salty compared to fresh waters. For comparison, Otisco Lake, also located in Onondaga County, has a salt content of about 0.03%, nearly 120 times lower than the ocean. Before Allied-Signal closed in 1986, the salt content of Onondaga Lake was unusually high, averaging 0.30%. This was ten-times greater than Otisco Lake.

“Natural” Salt Contributions

Some Central New Yorkers believe that most of Onondaga Lake's salt concentration results from natural inputs from nearby salt formations. This may seem plausible considering that the eastern and southern shores of Onondaga Lake supported a flourishing salt mining industry in the 19th century, but the salt mined then was taken from springs and wells located near the Lake's shore, not from the Lake's water.

Approximately 6 million pounds of salty wastes—chloride, sodium, and calcium—were discharged daily to Onondaga Lake from the soda ash facility before it closed. Scientific measurements of the salt concentrations in the lake and tributaries following the closure of the soda ash facility established that earlier assessments of "natural" salt contributions to Onondaga Lake were greatly overestimated. The concentration of chloride, the most important component of salinity to Onondaga Lake, has decreased significantly since the closure of the Allied soda ash facility.

Solvay Waste Beds

The salinity level of the lake is still artificially high because salty wastes are still entering Onondaga Lake from the Solvay waste beds located along Nine Mile Creek. The waste beds contain by-products of the company's soda ash production. Elimination of continued salt pollution inputs from waste beds would result in the total salt content of Onondaga Lake approaching 0.05%, which is much closer to the levels of other freshwater lakes in the area.

Effects of High Salinity

Salty wastes are discharged to Onondaga Lake from the Solvay waste Beds.

The discharge of salt and other wastes associated with the production of soda ash has had far-reaching effects on Onondaga Lake and the adjoining Seneca River system. The Lake's elevated salinity undoubtedly reduced the diversity of its aquatic life. High concentrations of calcium discharged to the Lake from soda ash production caused massive quantities of calcium carbonate to accumulate on the lake bottom. These deposits have accelerated the rate at which Onondaga Lake is filling in and eliminated habitats suitable to support a normal near-shore biological community.

Because salty water is denser than fresh water, high salt loadings also altered the natural stratification cycle in Onondaga Lake. The Seneca River, a moving body of water that ordinarily should not stratify throughout the year, also experiences chemical stratification as a result of receiving denser, salty water from Onondaga Lake. The stratification in both the Lake and the river contributes to a decline in the oxygen levels in both bodies of water.

Oncolite Formation

Much of the near-shore area of Onondaga Lake is covered with calcium carbonate stones called oncolites. Scientists who have investigated the oncolite phenomenon in Onondaga Lake have concluded that the high density of oncolites is related to the salt waste discharges of the Allied-Signal soda ash facility. The oncolites inhibit the growth of rooted aquatic plants. The scarcity of rooted vegetation greatly limits the populations and variety of animal species found in the Onondaga Lake.

Nonpoint Source Pollution 

Nonpoint source pollution refers to water pollution that does not originate from a single clearly identifiable source like a discharge pipe or drain. Nonpoint pollution originates over a broad area and a variety of sources.

Examples of nonpoint source pollution are:

Urban nonpoint source pollution, including street debris, lawn chemicals, and petroleum-based products such as motor oil, can reach the Lake and contribute to reduced aesthetics and water quality problems. Rural nonpoint source pollution includes sediments, pesticide- and fertilizer-runoff that is generated in a rural or agricultural setting.

Effects of Nonpoint Source Pollution

Because of its dispersed sources, nonpoint source pollution is difficult to control, and its effect on a water body is difficult to assess.

The effect of nonpoint source pollution on Onondaga Lake is under investigation. Activities that generate nonpoint pollution in the lake's watershed can lead to pollution in the Lake. Fertilizers contain phosphorus, which is one of the leading contaminants of concern for Onondaga Lake. Phosphorus leads to algae growth which affects the lake's water clarity. And when the algae die, oxygen is consumed which leads to depletion of oxygen in the Lake.