• Length: 100 Miles
• Surface Area: 24,000 Acres
• Average Depth: 10 Feet
Eagle Lake is a lake at 5,098 ft elevation in Lassen County approximately 15 miles north of Susanville, California. An endorheic alkaline lake, it is the second largest natural lake entirely in the state of California, United States.
Eagle Lake is home to osprey (Pandion haliaetus) and bald eagles (Haliaeetus leucocephalus), from which it gets its name.
Historically American white pelicans (Pelecanus erythrorhynchos) nested on Eagle Lake. They suffered from hunting by locals who mistakenly thought the pelicans ate the native trout and stopped nesting completely after 1932, when water was exported for agricultural irrigation and lowered the lake level by three meters, changing their nesting island into a less desirable peninsula ("Pelican Point").
Eagle Lake was once part of a large lake on the Modoc Plateau millions of years ago. The modern lake is 15 mi long by 1.8–2.5 mi wide and is highly alkaline (pH 8-9). The lake consists of three basins, two of them averaging 16–20 ft deep, the third averaging 32–65 ft and reaching a depth of nearly 98 feet.
The tributaries of Eagle Lake (beginning in the lake's north end and going clockwise) are Cleghorn Creek, Papoose Creek, Merrill Creek, and Pine Creek. Pine Creek is the main tributary of Eagle Lake and is 39 miles long. Now an intermittent stream; only the upper 6.8 miles of Pine Creek has perennial flow. In 1923 the Leon Bly Tunnel was constructed to export lake water to the Honey Lake Valley via Willow Creek, a tributary of the Susan River. The 2 mile long tunnel was cut through old lava flows but falling lake levels rendered it useless and a landslide partially blocked the tunnel entrance. However, a 1990 study found that lake water still flows through the tunnel although tunnel fish are from the Willow Creek assemblage.