Mono Lake, nestled in California’s Eastern Sierra Nevada, is a saline lake. Its waters, approximately 2.5 times saltier than the ocean and highly alkaline, host a distinct ecosystem. The lake is renowned for its tufa towers, mineral formations of calcium carbonate that rise from its surface, created by the interaction of freshwater springs and the lake’s chemistry. This environment supports trillions of brine shrimp and alkali flies. These tiny creatures form the base of a food web that sustains millions of migratory birds, making Mono Lake a significant stopover point along the Pacific Flyway.
The Great Water Diversion
Mono Lake’s fate changed in 1941 when the City of Los Angeles, through its Department of Water and Power (LADWP), began diverting water from the lake’s tributary streams. This action, designed to supply Los Angeles’s growing water demands, rerouted freshwater from Rush, Lee Vining, Mill, and Walker creeks. Over the next four decades, these diversions caused the lake’s level to drop by approximately 45 vertical feet, reducing its volume by half. The significant loss of freshwater inflow also doubled the lake’s salinity, altering its ecosystem.
Ecological Impact
The decline in Mono Lake’s water level and increased salinity had significant environmental consequences. The brine shrimp and alkali fly populations, forming the core of the lake’s food web, faced threats from harsh conditions, reducing their productivity. This disruption impacted millions of migratory birds, including California Gulls and phalaropes, that depend on these organisms. As the lake level fell, Negit Island, a critical nesting site for California Gulls, connected to the mainland by a land bridge. This allowed predators like coyotes to access nests, leading to declines in nesting success for the gull colonies.
The exposed lakebed dried and became a source of hazardous dust storms. This alkali dust, containing high concentrations of arsenic, posed a significant air quality and health risk to the Mono Basin region. Falling water levels also exposed the tufa towers, altering the lake’s distinctive landscape. These visible changes indicated the lake’s ecological challenges.
The Battle for Restoration
Concern over Mono Lake’s decline spurred environmental groups and citizens to act. The Mono Lake Committee, formed in 1978, became a leading advocate for the lake’s protection and restoration. This group, along with the National Audubon Society, initiated legal battles challenging the water diversions. A California Supreme Court decision in 1983, National Audubon Society v. Superior Court, affirmed the Public Trust Doctrine’s application to Mono Lake. This doctrine asserts that certain natural resources, including navigable waters, are held in trust by the state for public benefit and must be protected.
The legal precedent set by this ruling compelled a re-evaluation of water rights in the Mono Basin. In 1994, the California State Water Resources Control Board issued Decision 1631. This decision mandated a management level for Mono Lake at 6,392 feet above sea level, setting limits on LADWP’s water diversions to allow the lake to recover. Decision 1631 also established rules for tributary stream flows and outlined conditions for protecting public trust resources.
Mono Lake’s Ongoing Recovery
Following the 1994 decision, reduced water diversions have allowed Mono Lake’s level to rise. As of August 2025, the lake’s surface elevation was approximately 6,382.9 feet above sea level, an increase from its historic low but still below the mandated 6,392-foot management level. This increase in water volume has contributed to the slow recovery of the lake’s ecosystem, benefiting brine shrimp and alkali flies. Bird populations are returning, and improved lake levels have helped mitigate dust storms by re-covering portions of the exposed lakebed, enhancing air quality.
Despite progress, the lake continues to face challenges, including drought cycles and the remaining distance to reach its ecologically healthy management level. The ongoing efforts to restore Mono Lake demonstrate how balancing human needs with ecological preservation can lead to positive environmental outcomes. The lake’s story highlights the lasting effects of environmental policy and community advocacy.