California's historic drought

A tire rests on the dry bed of Lake Mendocino, a key Mendocino County reservoir, in Ukiah, California February 25, 2014. REUTERS/Noah Berger

A secret service agent looks over a farm field as President Barack Obama speaks to the media on California's drought situation in Los Banos, California February 14, 2014. REUTERS/Wally Skalij/Los Angeles Times/Pool

Cattle graze on hay in a landscape that would normally be covered in green grass on the Van Vleck Ranch in Rancho Murieta, California, February 12, 2014. REUTERS/Max Whittaker

A Caltrans information sign urges drivers to save water due to the California drought emergency in Los Angeles, February 13, 2014. REUTERS/Jonathan Alcorn

A tumbleweed is seen at an irrigation channel on a farm near Cantua Creek, California February 14, 2014. REUTERS/Robert Galbraith

A police officer mans a roadblock as smoke billows from a wildfire driven by fierce Santa Ana winds in Rancho Cucamonga, California April 30, 2014. The so-called Etiwanda Fire, a wind-driven brush fire burning out of control in drought-parched Southern California wildland, forced the evacuation of hundreds of residents in the northern part of suburban Rancho Cucamonga, officials said. REUTERS/David McNew

A tiny patch of snow sits in the shade of a tree at the site of a California Department of Water Resources snow survey in Phillips, California May 1, 2014. The reading at Phillips is zero, where it typically averages roughly 40 inches of snow on May 1, and the statewide snowpack water content is at 18 percent of average. REUTERS/Max Whittaker

Chief of Snow Surveys for the California Department of Water Resources Frank Gehrke measures the California snow pack in the Lake Tahoe region of California, January 30, 2014. REUTERS/James Glover II

A dock extends into the dry bed of Lake Mendocino, a key Mendocino County reservoir, in Ukiah, California February 25, 2014. REUTERS/Noah Berger

The remains of an automobile is pictured on the bottom of the Almaden Reservoir near San Jose, Calif., January 21, 2014. REUTERS/Robert Galbraith

Thousands of juvenile salmon are dispatched into a holding tank in the Sacramento River in Rio Vista, California March 25, 2014. REUTERS/Robert Galbraith

Farmer Sarah Woolf walks past a field of onions on her farm near Cantua Creek, California February 14, 2014. REUTERS/Robert Galbraith

A sign is shown by an empty boat marina at Folsom Lake, which is 17 percent of its capacity, in Folsom, Calif., January 22, 2014. REUTERS/Robert Galbraith

Mark and Ellen Fontaine stand beside water tanks at their home in Philo, California February 25, 2014. As drought conditions continue in Northern California, the couple now relies on water deliveries by truck to supply their home. REUTERS/Noah Berger

A flock of geese flies above the receding waters at Folsom Lake, which is 17 percent of its capacity, in Folsom, Calif., January 22, 2014. REUTERS/Robert Galbraith

A sign advising to pray for rain hangs above an exhibit area at the 47th Annual World Ag Expo in Tulare, California, February 12, 2014. The expo takes place as a third year of drought plagues California farmers with the driest year on record. REUTERS/David McNew

A sign is seen at an intersection near Cantua Creek, California February 14, 2014. REUTERS/Robert Galbraith

A stream of water trickles on the bottom of the Almaden Reservoir near San Jose, Calif., January 21, 2014. REUTERS/Robert Galbraith

A houseboat is removed from the receding water at Bridge Bay in Shasta Lake, which is 100 feet (30 meters) below its normal levels, in Shasta, Calif., January 23, 2014. REUTERS/Robert Galbraith

Visitors take photographs at the bottom of Folsom Lake, which is 17 percent of its capacity, in Folsom, Calif., January 22, 2014. REUTERS/Robert Galbraith

An excavator operator helps construct an emergency pipeline to increase supplies of potable water in Willits, California February 25, 2014. REUTERS/Noah Berger

Water falls from a drip line on display at the Eurodrip USA exhibit at the 47th Annual World Ag Expo in Tulare, California, February 12, 2014. REUTERS/David McNew

A visitor walks near the receding waters at Folsom Lake, which is 17 percent of its capacity, in Folsom, Calif., January 22, 2014. REUTERS/Robert Galbraith

The nearly dry bottom of the Almaden Reservoir is shown near San Jose, Calif., January 21, 2014. REUTERS/Robert Galbraith

Snow cover in the Sierra Nevada mountain range in California in January 2013 (L) and January 2014 is compared in this combination of NASA satellite handout photos. REUTERS/NASA