New York freshwater-wetland screening has separate state and federal steps. A map or old determination does not necessarily answer whether a proposed project needs a current state review. This guide describes the New York State Department of Environmental Conservation (DEC) process; it does not determine the status of a property or whether an ADU is allowed under local zoning.
Check DEC’s current application scope
DEC’s current guidance reflects an April 8, 2026 court decision affecting its freshwater-wetlands regulations. DEC says it continues to protect wetlands that remain jurisdictional under state law and will require applications for projects that would impact Previously Mapped Freshwater Wetlands and/or wetlands 12.4 acres or greater in size. Treat those as the application categories described by DEC’s current page, not as a parcel finding or a complete account of every federal, local, or other environmental requirement. Confirm current mapped status, boundaries, and project impacts with DEC before relying on a prior screen.
If DEC issued a freshwater-wetland jurisdictional determination (JD) for the property between January 1, 2025 and April 8, 2026, its current page provides a reassessment request route. Check that page and the linked request form to confirm whether the existing determination and the proposed work fit the reassessment process.
Request a Parcel JD
Submit a Parcel JD request for the property or a clearly described Area of Interest. DEC reviews the submitted information and may ask for more. Its current process uses aerial imagery and wetland mapping databases to assess whether regulated wetlands or adjacent areas are present in the requested boundary. DEC says it will send a letter with a positive or negative result within 90 calendar days.
A Parcel JD answers whether regulated wetlands or adjacent areas are present in that requested area. It does not map the full extent of a wetland. A negative New York JD applies to the area and state program addressed by the request; it does not rule out a federal Clean Water Act permit. The U.S. Army Corps of Engineers is the separate contact for federal wetland compliance.
Follow a positive result through the next checks
After a positive Parcel JD, wetland boundaries need to be delineated to assess where a proposal may affect them. DEC says an applicant can ask the regional office about a site delineation or hire an environmental consultant whose work DEC must verify. Field work has no stated completion deadline because weather and ground conditions can prevent a site visit; do not treat the 90-day Parcel JD period as a deadline for delineation.
DEC identifies a Project JD as the next determination for deciding whether the proposal may need a wetland permit. Give DEC the actual project location and work description: a determination based on a larger parcel or a different project footprint may not answer the question for the planned ADU. Keep the parcel boundary, request area, JD letter, delineation, project plan, and any agency response together.
Recheck DEC’s current guidance before design or submission, especially where an earlier determination predates the April 2026 decision. Then check local land-use, building, stormwater, and other environmental requirements separately. A DEC screening result does not establish zoning permission, an exemption, permit approval, or federal compliance.