Tens of thousands of farmed non-native Atlantic salmon are accidentally released into the wild in Washington waters in the 2017 Cypress Island Atlantic salmon pen break.

The Atlantic salmon is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to 1 m (3.3 ft) in length. Atlantic salmon are found in the northern Atlantic Ocean and in rivers that flow into it. Most populations are anadromous, hatching in streams and rivers but moving out to sea as they grow where they mature, after which the adults seasonally move upstream again to spawn.

Washington, officially the State of Washington, is a state in the Pacific Northwest region of the United States. It is often referred to as Washington State to distinguish it from the national capital, both named after George Washington. Washington borders the Pacific Ocean to the west, Oregon to the south, Idaho to the east, and shares an international border with the Canadian province of British Columbia to the north. Olympia is the state capital, and the most populous city is Seattle.

On August 19, 2017, a net pen at a salmon farm near Cypress Island, Washington, broke, accidentally releasing hundreds of thousands of non-native Atlantic salmon into the Pacific Ocean. The fish farm was run by Cooke Aquaculture Pacific, LLC. According to the Washington State Department of Natural Resources, inadequate cleaning was likely the primary cause for the pen break; the nets were supporting more than six times their own weight in biofouling. Coastal tribes were hired to fish the escaped salmon. Atlantic salmon farming was later banned in Washington state in reaction to the incident.