San Juan Islands Watershed

Location of the San Juan Islands Watershed in Washington State.  Map courtesy of the EPA.The San Juan Islands are a unique watershed, with no major rivers and a few streams fed only by groundwater and precipitation. Second-growth conifer forests, hardwood forests, shrub plants, prairie, and rocky beaches all occur on the islands, but forest is dominant over almost 70 percent of the county. The islands get less rainfall than the rest of Puget Sound, a result of the rain shadow from the Olympic Mountains and Vancouver Island. At the south end of Lopez Island, precipitation is around 19 inches annually, rising to 30 inches at the northern tip of Orcas Island. Because the only source of freshwater is rainfall, water availability is a concern.

The islands support over 291 species of birds, including the largest bald eagle population in the lower United States. Fresh- and salt-water wetlands provide important habitat for a number of species, as does the upland prairie found on several of the islands.

EPA watershed profile:

  • Counties: San Juan
  • National Estuary Programs: Puget Sound
  • Other Watersheds Upstream: None
  • Other Watersheds Downstream: None

Related WRIA: 02

All Puget Sound WRIAs


Department of Ecology


Friday Harbor, San Juan Island. Photo courtesy of NOAA and the Pacific Tides Party.

San Juan County Best Available Science Synthesis

A summary of data on ecosystems designated as Critical Areas (formerly Environmentally Sensitive Areas) in San Juan County, including recommendations for management.


Presentations: 2013 study panel on ecosystem-based management of forage fish in Puget Sound

Download presentations from the Study Panel on Ecosystem-based Management of Forage Fish held August 25, 2013 at the University of Washington’s Friday Harbor Lab, San Juan Island.

Camas flower in full bloom

Relic gardens: camas in the San Juan Islands

A botanist believes Coast Salish tribes once favored small islands in the San Juan archipelago for growing camas, an important food staple. Her studies may also show the vulnerability of these relic gardens to climate change as sea levels rise.