Eagle Lake is situated east of Lassen Volcanic National Park, just northwest of the town of Susanville. At 28,000 acres, it is the second-largest natural lake wholly in California (after Clear Lake, Lake Co.), and its closed freshwater environment supports an abundance of native fish, notably the Eagle Lake Rainbow Trout, a large subspecies wholly endemic to the lake. Extensive freshwater wetlands remain at the borders of the lake. Most of the land surrounding the lake is managed by the BLM and the USFS, and is surrounded by USFS land (Lassen National Forest). Since the mid-1970s, Eagle Lake has seen a surge in visitation by fisherman during summer, with most activity centered at its southern end. The surrounding landscape represents a transition from the Cascades on the south (pine forests) with the Great Basin desert on the north.
The waterbirds of Eagle Lake have been studied since the early 1900s, with major investigations in the 1970s (Gould 1974) and the late 1990s (Shaw 1998). It supports California's largest nesting colonies of Western and Clark's grebes (4-5000 pr., fide D. Anderson) and possibly Eared Grebe (>3000 pr. in 1997), and was identified by Shuford (1998) as one of 10 key breeding sites for Black Tern in California, supporting over 100 pr. in 1997 (but see Shaw 1998, who found fewer). Large concentrations of nesting Osprey and Bald Eagle (>25 and up to 10 pr., resp.) in the state are found here (D. Shaw, pers. comm.). Several sensitive forest species, including Northern Goshawk, Vaux's Swift and Willow Flycatcher, are known to breed in the Lassen National Forest surrounding the lake, but not within the lake basin itself. American White Pelican formerly nested on the lake's "Pelican Point", but have not been seen since more than 1000 birds were bludgeoned to death by fishermen in the early 1900s (see Shaw 1998). This species still over-summers in breeding condition and its re-establishment is conceivable given changes in management of the lake.
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Human visitation essentially doubled at Eagle Lake during the 1980s (Shaw 1998), and development pressure along its shoreline continues apace. Eagle Lake is an entirely closed system, with very little surface flow of water into the lake and no outlet to release exhaust inputs from recreational watercraft. Direct disturbance by boaters during the summer remains the most pressing threat to waterbirds, as well as to post-breeding dispersers from other sites around the Great Basin (e.g. pelican, terns). However, the fact that the original suite of inland seabirds (except for pelican) continue to breed at the lake, some in high numbers, suggest that its ecosystem remains somewhat intact.
Most of the land surrounding the lake is managed by the BLM and the USFS, and is surrounded by USFS land (Lassen National Forest).
Eagle Lake is a closed freshwater natural lake with extensive freshwater wetlands remaining at the borders. Lassen National Forest surrounds the lake.