Long Island Sound Comprehensive Conservation and Management Plan

Clean Waters and Healthy Watersheds


Improve water quality by reducing contaminant and nutrient loads from the land and the waters impacting Long Island Sound.

Clean water is the foundation of a healthy Long Island Sound—for human use and recreation, for thriving fisheries, and for productive habitats. The condition of the Sound depends on the quality of the waters draining from the landscapes surrounding it. This connection between the land and water, between healthy, sustainable upland communities and a healthy Long Island Sound is the foundation of the Clean Waters and Healthy Watersheds theme.

While Long Island Sound’s water is getting cleaner, the Sound still suffers from hypoxic “dead zones,” beach closures, and other effects of contamination that keeps the Sound from meeting water quality standards. Addressing these environmental conditions will require integrated approaches to reducing polluted storm and ground water, contaminants of emerging concern, and creating resiliency of infrastructure. There will also be a need for land use planning that protects water resources, which includes adaptation to changing climate, and ensuring the sustainable use of the Sound’s resources. Additional emphasis is needed on assessing and improving the water and habitat quality of the Sound’s embayments, where much of the public goes for recreation and enjoyment.

Controlling nitrogen pollution remains the top priority. The Total Maximum Daily Load Analysis to Achieve Water Quality Standards for Dissolved Oxygen in Long Island Sound (CT DEEP, NYSDEC 2000) set allocations for nitrogen among five watershed states. The plan also identified steps to evaluate additional nitrogen reductions and alternative technologies while continuing monitoring and research programs to assess attainment of water quality standards. Connecticut and New York are now meeting the nitrogen reduction targets for wastewater treatment facilities, the largest source of nitrogen, thanks to recent investments in upgrades. Nitrogen reductions from atmospheric deposition and agricultural sources are also meeting TMDL allocations. Nitrogen from on-site wastewater treatment systems, residential turf fertilizer applications and stormwater runoff, however, have remained level or increased. To continue progress in attaining water quality standards it is necessary to manage adaptively, continuing to seek aggressive and practical nitrogen reductions from all sources while evaluating their effectiveness. This is all the more important due to the changes in the ecosystem brought about by climate change that may make Long Island Sound more susceptible to hypoxia. With new information on the success of reducing nitrogen and the response of Long Island Sound to these reductions, the TMDL target will need to be assessed and revised as appropriate.

Ecosystem Targets

The following ambitious, but achievable, ecosystem targets have been developed to drive progress toward attaining the Clean Waters and Healthy Watersheds (WW) goal.

Extent of Hypoxia

Measurably reduce the area of hypoxia in Long Island Sound from pre-2000 Dissolved Oxygen TMDL averages to increase attainment of water quality standards for dissolved oxygen by 2035, as measured by the five-year running average size of the zone.

View Extent of Hypoxia Environmental Indicator

Nitrogen Loading

Attain wastewater treatment facility nitrogen loading at the recommended 2000 Dissolved Oxygen Total Maximum Daily Load allocation level by 2017 and maintain the loading cap. Have all practices and measures installed to attain the allocations for stormwater and nonpoint source inputs from the entire watershed by 2025.

View Nitrogen Loading Environmental Indicator

Water Clarity

Improve water clarity by 2035 to support healthy eelgrass communities and attainment of the eelgrass extent target.

View Water Clarity Environmental Indicator

Impervious Cover

Through green infrastructure, low impact development, and stormwater disconnections, decrease by 10 percent the effective area of impervious cover in the Connecticut and New York portions of the watershed by 2035 relative to 2010 baseline.

View Impervious Cover Environmental Indicator

Riparian Buffer Extent

Increase the percent area of natural vegetation within 300 feet of any stream or lake in the Connecticut and New York portions of the Long Island Sound watershed to 75% (1,030 square miles of natural vegetation) by 2035 from 2010 baseline of 65%.

View Riparian Buffer Extent Environmental Indicator

Approved Shellfish Areas

Upgrade 5% of the acreage currently restricted or closed for shellfishing by 2035 from a 2014 baseline.

View Approved Shellfish Areas Environmental Indicator

Sediment Quality Improvement

Reduce the area of impaired sediment in Long Island Sound by 20% by 2035 from 2006 baseline.

View Sediment Quality Improvement Environmental Indicator


  • Further reducing nitrogen pollution requires addressing sources that are smaller, more diffuse, or more distant from the Sound.
  • Polluted runoff from developed lands contaminates waters with pathogens, which result in closed beaches and restrictions on shellfish harvest areas.
  • Aging infrastructure leaks untreated sewage to coastal waters.
  • Water quality must be improved in bays and harbors to protect and restore submerged aquatic vegetation and benthic community health.


  • Reduce nitrogen from decentralized, on-site wastewater treatment systems (septic systems), and turf fertilizer applications.
  • Work with states and communities in the entire watershed, not just in Connecticut and New York, particularly on low-cost upgrades to centralized wastewater treatment facilities.
  • Document the economic and ecosystem consequences of nitrogen pollution from hypoxia, eelgrass and wetland loss, and increased vulnerability to acidification.
  • Implement smart growth and low impact development policies to minimize the environmental impacts of new development while green infrastructure is increasingly added to areas already developed.
  • Continue capital investments in wastewater treatment infrastructure.
  • Identify and control local pollution sources through community-based watershed monitoring (including citizen science) and protection programs.

What’s Being Done

Find examples below of actions being undertaken by LISS and its partners to achieve outcomes to help meet the ecosystem targets and achieve the Comprehensive Conservation and Management Plan goals for a healthier Long Island Sound.

Desired Outcome: Water quality is improved by reducing contaminant and nutrient loads discharged from the watershed to the Sound.
  • Connecticut and New York municipalities have prevented more than 50 million pounds of nitrogen pollution a year from entering Long Island Sound. Learn more on the role upgrading wastewater treatments plants had on the WWTP.
  • EPA, Connecticut and New York are working on achieving a cleaner Long Island Sound through new nitrogen pollution reduction strategies. Learn more in the Nitrogen Reduction Strategy web page.
  • Municipalities are looking at green infrastructure projects to reduce pollutants carried by stormwater from entering the Sound and its tributaries. Learn more in Taking Action for Healthy Watersheds web page.
Desired Outcome: Existing contaminants and nutrients are managed and removed, improving public health and water quality.
  • Extracting nitrogen through the harvesting of shellfish and seaweeds can lead to cleaner water. Learn more in the nutrient bioextraction initiative web pages.
  • The Long Island Sound Dredged Material Management Plan (LIS DMMP) is a comprehensive planning process and decision-making tool to address the management of dredged material for a specific harbor or navigation project, group of related projects, or geographic area. Learn more on the EPA website.
  • The  amount of toxic contaminants discharged into Long Island Sound have been sharply reduced. Learn more on the EPA Toxics Resource Inventory website.
Desired Outcome: Research, monitoring, and modeling to attain water quality objectives is maintained and improved.
  • LISS and its partners are developing a new generation of models to better describe dissolved oxygen concentrations as well as address new challenges such as warming temperatures, increasing precipitation and more development. Learn more in the Research section.
  • LISS and its partners maintain a long-term monitoring program in the open waters of the Sound, and are expanding efforts in harbors and bays. Learn more in the Research section.

For More Information
The full description of the actions, strategies, objective and outcomes for Long Island Sound Study can be found in the Comprehensive Conservation and Management Plan.

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