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The Lost Lake watershed (38°51'37"N, 120°5'48"W) is in the northern Sierra Nevada near Lake Tahoe in the Desolation Wilderness of the Eldorado National Forest. Research at Lost Lake began in 1989. The lake is shallow (mean depth 1.9 m) and small in comparison to the other lakes (V/A index, 0.05 m). During winter, the lake freezes to a depth of 1 to 2.5 m, representing 35-72 % of the lake volume. Ice typically formed in November and persisted until June.

Lost Lake has the smallest volume (12,500 m3) and surface area (0.7 ha) of the seven acid rain study lakes. Complete mixing of the lake took place in late spring and in the autumn. Thermal stratification occurs during the summer but is weaker than winter (inverse) stratification. Winter stratification is associated with near anoxia (dissolved oxygen ~ 0) in the hypolimnion during most winters; surface waters had O2 levels above 5 mg L-1 during other periods. Maximum lake temperatures ranged from 13°C (1993) to 21°C (1991). A healthy population of brook trout is present.

The Lost Lake watershed has the lowest elevation (2,475 m) and has the least vertical relief of the acid rain study catchments (160 m). There are two inflow channels and the watershed has a north-facing aspect. Hemlock, Lodgepole Pine and Western White Pine line the shore of the lake and are scattered, along with patches of shrubs, throughout the watershed. Several areas of wet meadows are found around the lake. Most of the remaining catchment is composed of bedrock or bedrock with small inclusions of grass-covered, Alpine Brown Soils.