SAN DIEGO -- State authorities are evaluating a controversial plan to bolster San Diego reservoirs with water from Imperial County farmers.

The Water Resources Control Board is holding a series of hearings over 20 days to review the environmental effects of a plan that supporters say will resolve San Diego's long-term water needs.

The water-rich but cash-poor Imperial County has offered to transfer a portion of its share of the Colorado River to San Diego for an annual payment of about $64 million.

The proposed annual transfer of 200,000 acre feet of water to thirsty San Diego would be the largest-ever farm-to-city water sale in the nation. It's scheduled to start next year.

Under the agreement, Imperial Valley farmers would come up with the water through conservation measures. But environmentalists fear that could mean a fatal decline in runoff to the ecologically fragile Salton Sea, the state's largest lake.

Another alternative would be for the farmers to leave fallow unneeded farm land, but some fear that could hurt the already depressed Imperial County economy.

The hearings are scheduled to begin Tuesday in the town of Holtville.