Department of Environmental Conservation

D E C banner

Cayuga Lake

Map of Cayuga Lake
Map of Cayuga Lake


The lake and watershed has been the focus of on-going monitoring by a number of groups, including the Finger Lakes Institute and the Community Science Institute. An additional monitoring study aimed at gaining a better understanding of the factors affecting nutrient loading in the lake, the Cayuga Lake Modeling Project, is also underway. A significant DEC monitoring effort, Water Quality Study of the Finger Lakes (PDF), provides a comparison of water quality in all the Finger Lakes.

Water Quality Issues

Aerial view of Cayuga Lake
View of Cayuga Lake - Bill Hecht

Water quality in much of Cayuga Lake is good, and meets water quality standards for the protection of recreational uses. The one exception to this assessment is in the shallow south end of the lake where sediment and nutrient loads from various sources result in weed and algal growth that impair summer recreational uses. Current water quality standards for water supply use of the lake are also being met. However, while DEC considers the lake to have water quality suitable for use as a water supply, this use has been assessed as threatened. This assessment is based on the NYS Department of Health Source Water Assessment Program (SWAP) evaluation of the potential, rather than actual, impacts to water supply use. The classification of much of the lake as a Class AA water, which designates the lake as suitable for use as a drinking water source requiring a minimum of treatment, makes the lake more vulnerable to potential sources. In the case of Cayuga Lake, the potential threats are due to considerable agricultural activity, wastewater sources, and other contributors of nutrients in the watershed. Elevated nutrient and chlorophyll levels in the lake may result in the formation of disinfection by-products (DBPs) in finished potable water that would require advanced treatment to meet drinking water standards. DBPs are formed when disinfectants such as chlorine used in water treatment plants react with natural organic matter (i.e., decaying vegetation) present in the source water. Prolonged exposure to DBPs may increase the risk of certain health effects.

The most recent water quality assessment of Cayuga Lake and its tributary waters can be found in Waterbody Inventory Priority Waterbodies List (WI/PWL) fact sheets.

South End Cayuga Lake
Aerial view of the south end of Cayuga Lake and Ithaca
South End Cayuga Lake - Bill Hecht

Water quality conditions in the South End of Cayuga Lake are much different than those in the rest of the lake. Whereas water quality in other parts of Cayuga Lake are generally good, the South End has experienced water quality problems dating back to the 1960s and has been assessed as impaired since 1998. Excessive algal and aquatic plant growth restrict recreational use of this part of the lake. Since the 1960s, aquatic plants, poor water clarity and other impacts have resulted in the continuous closure of Stewart Park Beach along the south end of the lake. More recently, increasing nutrient (phosphorus) levels and related algal and aquatic plant growth throughout the South End have been the dominant water quality issue.

There are a number of factors that contribute to conditions in the South End. For one, the South End is more shallow than the rest of the lake, generally less than 15 feet deep. In addition, the surrounding watershed in the South End is much more developed and more densely populated than other parts of the watershed. A number of larger tributaries (Fall Creek and Cayuga Inlet/Cascadilla Creek/Six Mile Creek) which carry significant nonpoint source pollution loads also empty into the South End. This portion of the lake also receives discharges from three large point sources: The Ithaca Area wastewater treatment plant, Cayuga Heights wastewater treatment plant, and the Cornell Lake Source Cooling Facility.

Invasive Species: Hydrilla

Hydrilla verticillatum (hydrilla, or water thyme) was discovered in Cayuga Inlet in August of 2011. Hydrilla has created significant ecological and economic problems throughout the country, and is particularly challenging to control due to abundant and persistent modes of reproduction, spread, and transport. The discovery of this highly invasive aquatic plant In Cayuga Inlet prompted immediate and forceful action, due to the great concern that this plant could move into Cayuga Lake and the Great Lakes ecosystem. A state and local task force was quickly established to delineate the hydrilla populations, identify appropriate management actions, and proceed with an aggressive strategy to eradicate the 166 acre infestation found in the Inlet and some connected waterways, using federal, state, and local resources. Key members of the task force include the City of Ithaca, the Tompkins County Soil and Water Conservation District and Department of Health, Racine-Johnson Aquatic Ecologists, DEC, Canal Corps, and other local and state organizations. Recommendations of the Task Force led DEC to conduct emergency rule-making to allow for a hydrilla infestation treatment effort. The Task Force is engaged in a multi-pronged eradication strategy, including the use of aquatic herbicides, hand removal, boat inspections, and extensive public education, outreach and monitoring. More information about hydrilla in Cayuga Inlet can be found on the Tompkins County CCE website (see link at right).

Watershed Management Actions

In 2001, a collaboration of local municipalities, community groups, interested citizens, and regional planning boards completed a management plan, the Cayuga Lake Watershed Restoration and Protection Plan (RPP) for the protection of the Cayuga Lake watershed. This effort coincided with the establishment of the Cayuga Watershed Intermunicipal Organization, a voluntary partnership of 31 villages, towns, cities and counties in the watershed working together to implement the RPP (see links at right). The main purpose of the RPP is to serve as a working guide for the public, elected officials, farmers, the business community, environmentalists and others to manage Cayuga Lake's valuable water resources.

South End Cayuga Lake Total Maximum Daily Load (TMDL)

DEC continues to work with local partners in the watershed to address current and potential sources of pollution and impairment to the Lake, particularly the South End. DEC has already worked with area municipalities to reduce wastewater point sources and stormwater nonpoint sources of nutrients to the lake. Currently, DEC is focused on developing and implementing a more comprehensive plan to address algal growth and other recreational impairments in the South End of the lake. The centerpiece of this approach is a TMDL analysis that will look at all sources of nutrients to the lake and determine necessary reductions to restore uses in the South End. This analysis will rely on a number of components, including a whole lake monitoring and modeling effort to determine the fate and movement of nutrients in the lake, and a watershed model to evaluate nutrient loads from tributary watersheds.

The SPDES permit addresses water releases from Cornell University's Lake Source Cooling facility. The permit includes a limit on the amount of phosphorous the facility draws from the deeper lake and discharges to the shallower southern shelf. An interim limit holds Cornell's discharge of phosphorus at its current levels. Once the TMDL is completed, a final limit will be developed based on the results of the TMDL. The permit also includes a requirement outlining Cornell's commitment to fund the water quality/modeling study to assist DEC with the development of the TMDL. The permit also contains other requirements, including Cornell's optimizing the use of the Lake Source Cooling while minimizing the volume of water that is drawn through the system and discharged to the southern shelf, outfall redesign/relocation evaluation, and biological/entrainment studies. Final reports and other permit deliverables related to these permit requirements are available.

The Cayuga Lake Modeling Project

The Cayuga Lake Modeling Project (CLMP) is a detailed study of the sources and fate of phosphorus in Cayuga Lake. The primary goal of this project is to build a computational water quality model of Cayuga Lake and its watershed, providing a better understanding of where phosphorus comes from, and how it affects the lake ecosystem. The CLMP began in 2013. Progress and developments regarding the CLMP have been shared with the public through periodic public meetings and regular meetings with local stakeholders.

Sign up for DEC Delivers

Enter email address:

Outreach and Additional Information

DEC continues outreach efforts and information sharing with local stakeholders throughout the TMDL development process for the South End Cayuga Lake. These activities build on existing local stakeholder outreach efforts:

  • DEC participation in regular Tompkins County Water Resources Council (see link at right) Monitoring Partnership conference calls, providing a point of contact for local access to DEC for Q&A and updates.
  • A Technical Advisory Committee (TAC) to provide independent advice and expertise to NYSDEC on scientific and technical aspects associated with lake water quality issues and the development of the model and TMDL for phosphorus in Cayuga Lake. The focus of the TAC is outlined in the TAC Charter (PDF), which was adopted when the TAC was initially formed (the Charter has been periodically updated, most recently in March 2015). The TAC will meet periodically to review progress and identify issues for presentation and discussion. A matrix of the technical issues raised through the TAC, along with responses from the CLMP investigators, is also available.
  • Periodic public meetings scheduled around key project milestones and used to report to the larger public on progress of the study and TMDL development, as well as other Cayuga Lake Watershed issues and activities. A public meeting schedule and recap of past public and TAC meetings is available.
  • Additional stakeholder involvement will also be conducted to coincide with the actual TMDL development process, which will commence when the Cayuga Lake Water Quality Modeling Study is completed at the end of 2016.

In addition, continue to check back here on the Cayuga Lake Watershed webpage, or contact us directly if you have other questions or need more information.

Facts About the Lake

Cayuga Lake is the second-largest of the Finger Lakes of central New York State, extending over 38 miles in length with an average width of 1.75 miles. It is one of the deepest of the Finger Lakes, with a maximum depth of 435 feet. The watershed draining into Cayuga Lake is the largest of the Finger Lakes, covering 785 square miles (approximately 500,000 acres) in parts of 6 counties (Cayuga, Tompkins, Seneca, Schuyler, Tioga and Cortland) and is home to 120,000 people. The watershed consists of agricultural, residential, industrial, and forested land. More than 140 streams flow into the lake along its 95 mile shoreline. The largest of these tributaries includes Salmon Creek, Fall Creek, Cayuga Inlet (including Cascadilla Creek and Six Mile Creek) and Taughannock Creek. Most of the lake is classified as being suitable for use as a drinking water supply (Class AA(T), A(T), or A); a small portion of the lake at the northern/outlet end is Class B(T).

More about Cayuga Lake: