East Okoboji Lake is a natural body of water, approximately 1,835 acres (7.43 km2) in area, in Dickinson County in northwest Iowa in the United States.

The towns of Spirit Lake and Okoboji, founded as European-American settlements in the nineteenth century, sit along its western shore.

They became notable after the Spirit Lake Massacre of 1857, when a renegade band of Sioux attacked the frontier settlements, in part for food, because they were suffering starvation during a severe winter with heavy snows.

Geologically, the lake, like its neighbors, is a glacial pothole, a remnant of the most recent ice age approximately 13,000 years ago.

[2][full citation needed] The lake was the main setting of the fourth X-Files episode, "Conduit".