King County, WA Environmental Rules: Coastal Development (2026)

King County's coastal development rules implement the Washington Shoreline Management Act (RCW 90.58) and the state Shoreline Master Program guidelines (WAC 173-26). Shoreline jurisdiction includes all marine waters of Puget Sound and the upland area within 200 feet of the ordinary high water mark, plus associated wetlands and floodplains. The county's SMP is codified inside K.C.C. Title 21A and the Critical Areas Ordinance at K.C.C. Chapter 21A.24, which establishes marine-shoreline buffers of approximately 115 to 165 feet from the OHWM depending on the environment designation (Natural, Conservancy, Rural, Residential, High Intensity, Aquatic). Building structures must be set back at least 15 feet from the edge of any required critical-area buffer under K.C.C. 21A.24. Bulkheads, docks, piers, dredging, fill, shoreline armoring, and most new structures within shoreline jurisdiction require a Shoreline Substantial Development Permit, a Shoreline Conditional Use Permit, or a Shoreline Variance, plus state Department of Ecology review. Single-family residences below the cost threshold can sometimes be exempt under WAC 173-27. Confirm with King County DLS - Permitting at 206-296-6600 and the Department of Ecology Northwest Regional Office.