HAILEY, Idaho (AP) - The Idaho Department of Water Resources has declared a drought emergency in Blaine County in central Idaho.      Gov. C.L. "Butch" Otter signed the order on July 16.     Agency Director Gary Spackman says the order will allow temporary changes in points of diversion, place of use and purpose of use for existing water rights.     Officials say the snow packs that feed the Big Wood River and Little Wood River have already melted a month early, leaving stream levels 20 to 70 percent below normal.      The drought order includes water in Fish Creek Reservoir. Wildlife officials are trying to salvage fish in the reservoir because fish are dying as water levels drop.