Three Mile Canyon Island is on the Columbia River above John Day Dam near the Town of Boardman (OR), and is owned and managed by the U.S. Army Corps of Engineers. Three Mile Canyon Island is a 17-acre island that was created by the John Day Dam impoundment. A dike-like barrier built from dredged material along its length protects an adjacent bay and boat launch. Currently there is a large California gull colony and smaller ring-billed gull colony on Three Mile Canyon Island, estimated to consist of a total of about 4,600 breeding pairs in 2009. The first documentation of Caspian terns nesting on Three Mile Canyon Island was in 1977 (184 breeding pairs), and the colony grew to nearly 300 breeding pairs by the late 1990's. In 2000 and again in 2001, no tern chicks were fledged from the island due to mink predation. The site was abandoned by nesting Caspian terns in 2002 and they have not nested there since, presumably because of the disturbance associated with mink activities on the island.
