[1][4] The lake fills a depression in the Siltcoos River watershed about 3 miles (5 km) from the Pacific Ocean south of Florence along U.S. Route 101.

The lake formed during a rise in sea level during deglaciation, when sand dunes were emplaced, blocking the flow of the lower reaches of several of Oregon's coastal rivers.

Covering about 7 square miles (18 km2), Woahink Lake's drainage basin lies between a dune complex, part of Oregon Dunes National Recreation Area, on the west and foothills of the Oregon Coast Range on the east.

Rainfall averages 80 inches (2,000 mm) a year, and coniferous forest covers much of the undeveloped land.

Species include largemouth bass, rainbow and coastal cutthroat trout, yellow perch, and others.