In 1941, the city of Los Angeles diverted water from the Owens River and three of four tributaries that fed Mono Lake in an effort to meet its increasing water demands. At the time Mono Lake was 2105 masl and salinity was 50000mg T1 (50%). By 1982, however, lake levels had fallen to 2091 masl and salinity had almost doubled to 99 000mg l_1 (99%) due to the water diversion. Shrinking water levels caused land-bridges to form between the mainland and islands, allowing coyotes and other predators' access to California Gull nesting sites. As well, due to increasing salinity, Mono Lake's brine shrimp (Artemia monica) was being considered for listing as a federally threatened species by the U.S. Fish and Wildlife Service.
Lowered water levels also exposed tufas, irregular shaped thick towers of calcium carbonate, endemic to this lake. Tufa rock is the primary substrate on which the aquatic larvae and pupae of Ephydra hians (alkali fly) are found. These flies are a dietary staple for many migratory birds that spend time at the lake. Falling lake levels also created a smaller shallow area around the lake (littoral zone). This meant less suitable habitat for fly larvae and pupae, declining fly numbers and therefore less food for migratory birds. Alkali flies, like brine shrimp, were threatened by increasing salinity as well. Concerted conservation efforts by the Mono Lake Committee, however, paid off. In 1983, the California Supreme Court ruled that under the public trust doctrine of the State's constitution, the State of California must protect natural resources like Mono Lake. As a result, Los Angeles currently takes only 16% of the original water diversion. Today, the lake stands at 2095 masl and in another eight years the water level is expected to rise another two meters. Rising water levels have covered the old land bridges preventing coyote access to gull nesting sites and decreasing salinity means the lake is once again teeming with brine shrimp and alkali flies which feed migratory birds. Mono Lake is an ecological success story that hopefully will be repeated worldwide.
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