Water quality monitoring Latest water quality information Facts from the biological program Fish monitoring—you can participate Live water quality data from the Lake Monitoring locations

Parties working with WEP Posters—Learn about the lake Archive: Past features Archive: AMP reports Archive: AMP data sets Photo galleries

Latest water quality information

Onondaga Lake: Progress Report 2007, issued June 2008
After more than a century of pollution from municipal and industrial waste, Onondaga Lake is responding to the large investment of funds in wastewater treatment with cleaner water. Pollution levels are down, and the conditions for aquatic life, especially fish, have improved.

Comments on this report are encouraged and may be directed to Joseph J. Mastriano, Operations Manager. Click here to email, or phone 315-435-2260.

What do the latest data show?

Onondaga Lake water quality continues to improve in response to reduction in nutrient loading from the wastewater treatment plant. However, the 2006 Lake conditions demonstrate the effect of a wet year on nutrient loading. Nonpoint source phosphorus input to the Lake increased in 2006 as a consequence of the above-normal precipitation and runoff. In response, Lake phosphorus and algal abundance showed a slight increase over 2005 conditions.

Dissolved oxygen content of the Lake has increased to the point where water quality standards are now routinely met during fall mixing. Algal blooms are diminishing and cyanobacteria (blue-greens) represent a minor component of the algal community. Improvements in the Lake have allowed the beds of aquatic plants to greatly expand; this has increased the amount of nesting and nursery habitat for the warmwater fish community.

Improvements in wastewater treatment

Average ammonia-N concentrations in Metro Outfall 001, seasonal basis, 1995-2006

Improvements to the county's wastewater collection and treatment system at the Syracuse Metropolitan Wastewater Treatment Plant (Metro) are primarily responsible for the improved water quality conditions in the Lake. Significant investment in wastewater treatment technology has achieved far lower discharges of wastewater-related pollutants, particularly ammonia and phosphorus.

Onondaga Lake had exhibited high ammonia concentrations for decades. Monitoring results from 1970 to 2002 documented that ammonia levels in the Lake waters were above New York State's ambient water quality standards designed to protect aquatic life. Effluent from Metro was the largest source of ammonia to the Lake, averaging about 90% of the total annual input. Recent improvements to Metro were designed to reduce ammonia levels in the treated effluent and bring the Lake's water quality into compliance with state standards.

The final stage of the Metro improvements for ammonia treatment came on-line in early 2004. The biological aerated filter (BAF) system has resulted in year-round nitrification (conversion of ammonia to nitrate) in wastewater. Prior to this final stage, various improvements to the treatment system had resulted in substantial reductions, particularly in the summer ammonia levels.
 

Average daily phosphorus discharge from Metro, 1990-2006

Enhanced phosphorus removal from wastewater is another objective of the Metro improvements currently underway. A high-rate flocculated settling (HRFS) physical-chemical treatment system (known as Actiflo) came on-line in 2005 to reduce effluent total phosphorus (TP) concentration.

This stage of phosphorus treatment is designed to meet a 12-month rolling average TP limit of 0.12 mg/L. Evaluation of compliance with this limit began in April 2006, following 12 months of operation. In 2006, Metro effluent TP concentration met the 0.12 mg/L limit.
 

In 2006 Metro contributed about 29% of the total external phosphorus load to Onondaga Lake through outfall 001 (26%) and outfall 002 (2.7%). The remainder of the phosphorus load came from nonpoint sources throughout the 285 square mile watershed.

Water quality monitoring results

Bacteria concentrations were monitored at a network of nearshore stations as well as at South Deep (the primary water quality monitoring site). In 2006, bacteria concentrations within the Class B portion of Onondaga Lake met the New York State ambient water quality standard for fecal coliform bacteria, which is meant to assess suitability for water contact recreation. However, concentrations in the Class C portion of the Lake, near the major southern tributaries and Metro discharge, were elevated following storms during the rainy summer of 2006. This result highlights the need for continued progress with CSOs, as well as the need for improved storm water management to reduce nonpoint source pollution from urban areas.

Dissolved oxygen (DO) levels continued to show improvement in response to reduced productivity in the Lake. The DO concentrations in surface water during the fall mixing period, a historically critical period in Onondaga Lake, were in compliance with regulatory standards.

Phosphorus concentrations in the Lake are declining as loading reductions are achieved at the wastewater treatment plant. In 2006, the summer average total P concentration was approximately 39 µg/L in the Lake's upper waters.

Chlorophyll-a concentration averaged 16.5 µg/L during the summer of 2006; the annual peak of 35 µg/L was measured at the end of March. Spring algal blooms are typical in Onondaga Lake. Moderate and variable algal levels were measured through much of the summer recreational period; slightly more than half exceeded 15 µg/L, the state-designated threshold of impaired suitability for recreational use. In 2006, cyanobacteria comprised about 2% of the total algal biomass. Nuisance algal blooms have been steadily diminishing, presumably in response to reductions in nutrient loads.

Water clarity of the Lake is variable both within and between years. A spring clear-water phase was evident from the mid-1990s through 2000 but is no longer typical. The loss of the clear water phase is attributed to biological factors, cascading from the proliferation of the alewife, as discussed below.

Biological monitoring results

Zooplankton grazing is a significant factor affecting water clarity. Throughout the 1980s and 1990s, a spring clear-water phase was attributed to a seasonal peak in the abundance of larger zooplankton. However, larger zooplankton are now essentially absent from the Lake, and the spring clearing events have disappeared as well. Larger zooplankton, which are efficient grazers of phytoplankton, are the preferred food source of the fish species alewife. The reduction in population of the larger zooplankton taxa was evident in late summer 2002 when young-of-the-year alewives first became abundant. Alewives are now prolific in the Lake, and their effects are seen throughout the food web. Destruction of larger zooplankton by alewives caused a decline in total zooplankton biomass from 2003 to 2005 and a diminution in their average size. The average size of zooplankton is gradually improving from the minimum values measured in 2003.

Fish are one of the most visible components of the ecosystem. Results of the 2006 fish program indicate that the community continues to be dominated by warmwater species. Popular gamefish such as largemouth and smallmouth bass are common and tend to be more abundant in the northern basin. This spatial pattern is consistent with the distribution of aquatic plants and macroinvertebrates, demonstrating that the northern basin provides better habitat quality. Other gamefish, such as walleye and northern pike, are present but are far less common than bass. Panfish, such as yellow perch, pumpkinseed, and bluegill, are abundant in nearshore areas.
 
Of the twenty-nine fish species captured in Onondaga Lake in 2006, thirteen (45%) showed evidence of successful reproduction. The young-of-the-year community was dominated by largemouth bass, which represented 49% of the catch. Overall abundance of young fish was notably lower in 2006 compared with 2000-2005 results.
 
Alewife abundance was evaluated using hydroacoustics, gill nets, and electrofishing. Length frequency analysis indicated that a strong year class of alewife was produced in 2005 and is augmenting the strong 2002 year class. Abundance of alewives is high compared with regional lakes.
 
The New York State Department of Health (NYSDOH) produces an annual report detailing advisories for the consumption of fish and game in New York. The May 2007 report, "2007-2008 Health Advisories: Chemicals in Sportfish and Game," included a significant revision. The NYSDOH now advises that largemouth and smallmouth bass greater than 15 inches in length from Onondaga Lake should not be consumed because of elevated mercury concentrations.

Macrophytes (rooted aquatic plants and algae) have changed profoundly in recent years. The number of species has increased from five in 1991 to seventeen in 2005, although the community is still dominated by a few species. Percent cover of macrophytes increased about three-fold between 2000 and 2005. Year-to-year variability is evident from the annual aerial photographs; this variability is typical of other regional lakes. Much of the littoral zone has plant coverage within the ideal range for largemouth bass propagation. A notable feature of the 2006 macrophyte abundance was a collapse in July, most likely due to extreme rainfall and associated runoff.

Tributary macroinvertebrates were monitored in 2006. The combination of habitat degradation, nonpoint source pollution, and CSO discharges affects the streams' macroinvertebrate communities. In 2006 the macroinvertebrate communities of Onondaga Creek, Ley Creek, and Harbor Brook showed varying levels of impact. Sites in Ley Creek tended to be the most severely affected followed closely by Harbor Brook. Sites in Onondaga Creek tended to be the least affected. Only minor changes to the macroinvertebrate community have occurred since completion of baseline surveys in 1999-2000.

Seneca River monitoring results

Onondaga County completed a focused water quality monitoring effort at selected stations along the Seneca-Oneida-Oswego river system in 2006. The wet summer of 2006 kept stream flow high in the Seneca River through most of the summer and prevented violations of ambient water quality standards for ammonia-N and nitrite-N. Frequent measurements using sondes detected brief periods where DO concentrations dropped below the standards. The river's water quality conditions continue to be strongly influenced by zebra mussels.

About the monitoring program

Onondaga County Department of Water Environment Protection (WEP) conducts an annual program to evaluate the water quality conditions of Onondaga Lake, the lake tributaries, and a portion of the Seneca River. An Amended Consent Judgment signed in 1998 requires Onondaga County to complete three major tasks: to upgrade treatment at the Metropolitan Syracuse Wastewater Treatment Plant (Metro), to mitigate the combined sewer overflows (CSOs), and to implement an Ambient Monitoring Program (AMP) to track the effectiveness of these improvements to the wastewater collection and treatment infrastructure. The AMP builds on Onondaga County's historical monitoring program, which provides a basis for evaluating trends over time. Each year the County prepares an annual report of its findings.

The AMP is designed to identify sources of materials (nutrients, sediment, microorganisms, and chemicals) to the lake, evaluate in-lake water quality conditions, and examine the interactions between Onondaga Lake and the Seneca River. In addition to the water quality-related program, the AMP examines many levels of the biological community of the lake and its watershed. The AMP includes an assessment of zebra mussels, benthic macroinvertebrates, aquatic plants, phytoplankton, zooplankton, and fish.

A rigorous quality assurance/quality control program is in place. Results of internal and external audits, blanks, and duplicates are presented in the annual AMP report. Samples are collected by trained technicians and analyzed in a state-certified laboratory. The annual AMP work plan is subject to New York State Department of Environmental Conservation (NYSDEC) review and approval. Technical experts (the Onondaga Lake Technical Advisory Committee) review the program findings and interpretive reports each year.

Technological advances enable the County to monitor water quality on a near-real-time basis. A water quality buoy with an array of probes that measure physical and chemical characteristics of the lake water is deployed on the lake at its deepest point (referred to as the South Deep station). Data from the buoy provide a window into how the lake quality changes in response to winds and waves. Acoustic Doppler devices, installed at the lake's outlet by the U.S. Geological Survey, provide data needed to assess water exchange between the lake and the Seneca River.

As part of the annual AMP, WEP tests over 20,000 water samples and examines several thousand biological samples. The new data have been appended to the custom long-term database developed by Dr. William W. Walker, Jr. The database, which merges the County's tributary and lake data from 1968 to the current year, has greatly improved data management and reporting tasks.