Mono Lake

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Mono Lake

Clear, cold water tumbles from snowcapped peaks and alpine fields at 13,000 ft (4,000 m) down the precipitous eastern escarpment of California's Sierra Nevada. The water feeds semi-arid, sagebrush–covered Mono Basin and, at the basin's heart, majestic Mono Lake. This is a salt lake with an area of 60 square miles (155 km²) at an elevation of 6,400 ft (2,000 m), and mountain waters have flowed to it for at least the past half million years, making it one of the oldest lakes in North America.

Mono Basin lies in the rain shadow of the Sierra Nevada; shielded from moist Pacific air masses to the west, it has a semi-arid climate . Being surrounded by higher ground, it also has no natural outlet. Over the millennia, the major water loss from Mono Lake has been by evaporation, a process that removes pure water and leaves dissolved salts behind, and the water in the lake has become alkaline as a result and two and a half times saltier than sea water.

The salty, alkaline lake water excludes fish, but it does provide ideal conditions for several life forms that normally are uncommon to inland waters. Algae blooms in abundance during winter, sometimes turning the lake water pea–soup green, and it provides summer sustenance to a profusion of brine flies and tiny brine shrimp. Brine flies and brine shrimp make Mono Lake a summer haven for hundreds of thousands of nesting and migratory birds. The lake's islands provide safe nesting for tens of thousands of California gulls and snowy plovers. Nearly 90% of the state's population of California gulls, which live mainly along the Pacific coast, are hatched on these islands. More than 70 species of migratory birds use Mono Lake—most notably, several hundred thousand eared grebes which stop over during their fall migration , and more than 100,000 phalaropes which come from South America for the summer.

Mono Lake's aquatic chemistry , combined with its unusual geologic and topographic environment , has given rise to the lake's signature feature: tufa towers. Tufa is a type of limestone which consists of calcium carbonate that forms around fresh water springs emanating from the lake bottom. Calcium carried by the spring water combines with carbonate in the alkaline lake to form soft rock masses that slowly grow into underwater pinnacles. These towers were almost entirely covered by water until recently; they were first exposed when the lake level started dropping in the early 1940s, because the growing city of Los Angeles had begun intercepting fresh water from streams feeding the lake and diverting it south to the city in a 250–mi (400 km) long aqueduct.

By the mid-1980s, Mono Basin supplied nearly 20% of the water used by Los Angeles, and the lake level had dropped more than 40 ft (12 m). As the water level dropped, the lake's salinity increased and shoreline habitat for brine flies decreased. Tufa formations became more exposed, dust storms grew more frequent and severe, and predators occasionally found access to island nesting sites. Meanwhile, California created the Mono Lake Tufa State Reserve, and
the United States Congress established the Mono Basin National Forest Scenic Area.

Ultimately, the demand for water by Los Angeles clashed with the demands of environmental groups, who sought to maintain Mono Lake's ecological integrity and the fish habitat of streams feeding the lake. Lawsuits have been fought in state and federal courts, and in 1989 California's State Supreme Court ordered the Los Angeles Department of Water and Power (LADWP) to reduce the amount of water it was diverting from the lake. In 1993, the State Water Resources Control Board recommended that the diversion be cut again, this time by half. LADWP has disagreed, arguing that Los Angeles needs the water and that the reduction is neither ecologically necessary nor economically wise.

The war over eastern Sierra water began at the turn of the twentieth century, when Los Angeles acquired rights to water previously used by farmers and ranchers in the Owens Valley, just south of Mono Lake. By mid–century the battleground had spread north to Mono Basin, and the war promises to continue well into the next century.