Turnagain Arm

The Cook Inlet is a large inlet of the Gulf of Alaska in south-central Alaska. It stretches for approximately 195 miles or 310 kilometers southwest to northeast, separating the Kenai Peninsula from mainland Alaska. It branches into the Knik Arm and Turnagain Arm at its northern end, on either side of Anchorage.

The inlet was first explored by Europeans in 1778 when James Cook sailed into it while searching for the Northwest Passage. It was named after Cook in 1794 by George Vancouver, who had served under Cook in 1778.

Its watershed covers about 40,000 square miles or 100,000km² of southern Alaska east of the Aleutian Range and south of the Alaska Range, receiving the Susitna and Matanuska rivers. The watershed includes the drainage areas of Mount McKinley. Within the watershed there are four active volcanoes and seven national parks. The inlet provides navigable access to the port of Anchorage at its northern end, and smaller Seward further south. Approximately 400,000 people live within the Cook Inlet watershed.