Mercer Island Waterfront Docks: Building Permits, Regulations and Rules

Building and maintaining waterfront docks and moorage in Mercer Island can be a complicated process. Property owners must comply with city, state, and federal agencies to make sure that the permitting process and all applicable regulations are followed. There are a plethora of details involved, but here are some quick notes.


1 dock per lot with minimum 40 ft of waterfront
8 feet wide maximum, 100 feet long maximum (exception for shallow water)
Setback 10 feet from lateral property line, 35 feet from adjoining moorage
Maximum height 5 feet over the water (OHWM), with 3 additional feet for handrails, storage, etc.

Covered Moorage:

Maximum covered moorage of 600 square feet coverage
Maximum height of 10 feet above the water
No closed side/walls allowed

A Note on Grandfathered docks/moorage: Many docks on Lake Washington don't comply with current regulations. Most of these docks are "grandfathered in", and are allowed to remain in place. Any alterations or maintenance of such docks, however, should always be preceded with an authorization by the applicable government agencies. Unauthorized changes could jeopardize a homeowner's ability to used the dock or even keep it at all.

All planning for the development or construction of docks and moorage should be started directly with the Planning Department at the City of Mercer Island.  Possible required permits include:

  • King County Substantial Development Permit
  • WA Department of Ecology (Washington's Shoreline Management Act)
  • WA Hydraulic Project Approval (Dept of Fish and Wildlife)
  • US Army Corps of Engineers, U.S. Fish and Wildlife (Endangered Species Act)
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November 15 2010 - Mercer Island
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