Assessing Water Quality in NY
The Clean Water Act (CWA) requires states to assess and report on the quality of their waters, every two years. Water quality reporting under CWA Section 305(b) and 303(d) are highly visible ways of communicating about the health of the nation’s waters. Water quality assessment under Section 305(b) is the assessment of all of the waters in the state and whether or not they are able to support their best use(s) (source of water supply, shellfishing, primary and secondary contact recreation, and fishing) in accordance with the state’s adopted water quality standards. Waters that do not support their best use(s) in accordance with water quality standards are reported to EPA in accordance with CWA Section 303(d) and are prioritized for the development of a Total Maximum Daily Load (TMDL).
To assess a waterbody, DEC considers all available water quality data. Data sources include but are not limited to data collected by NYSDEC, stakeholders, local, state, and federal governments, and Indian Nations. New York has established a data solicitation period to assemble all available water quality data. Starting in May and running through September of every odd year, the Division of Water solicits the public for data that can be used to update the WIPWL. The data solicitation is announced weekly in the DEC Environmental Notice Bulletin and MakingWaves. Water quality data submitted to DEC for use in updating assessment must meet the data requirements described in the Consolidated Assessment and Listing Methodology (CALM).
Consolidated Assessment and Listing Methodology
For more information about how water quality assessments are conducted, read the New York State Department of Environmental Conservation's Consolidated Assessment and Listing Methodology (CALM, updated May 2023) (PDF).
Previous versions of the CALM have been archived and are available upon request to [email protected].
Waterbody Inventory/Priority Waterbodies List
Waterbody assessment data are maintained in the Waterbody Inventory/Priority Waterbodies List (WI/PWL). The WI/PWL is used to prepare the Section 305(b) Report on Water Quality, and the Section 303(d) List of Impaired Waters Requiring a Total Maximum Daily Load. Additionally, the WI/PWL is used to develop waterbody segment factsheets which are available on DECinfo Locator.
The WI/PWL is also represented geospatially as a GIS layer and is made available for download via New York State GIS Clearinghouse. The WI/PWL GIS layer is updated every two years to align with the assessment results issued as part of Section 305(b) Report on Water Quality. View instructions for accessing WI/PWL factsheets via the DECinfo Locator.
