Idaho is in the midst of its worst drought in 50 years.

Three parched summers and two skimpy winters have sucked Idaho's reservoirs dry, killed hundreds of thousands of fish, wilted crops, scorched lawns and fueled a bevy of huge wildfires.Nothing similar has confronted modern-day Idaho since the 1930s, when four consecutive years of drought descended on the state. And even then, stream flows were slightly higher than in 1987 and 1988.

Many reservoirs in the upper Snake, Boise and Payette river basin are close to or have reached their lowest points in history.

The Boise, South Fork Payette and main Salmon rivers are running at all-time lows. The upper Snake reservoir system is carrying only 8 percent of capacity. The Boise system has 13 percent of capacity. Normal in October is 50 percent.

Weather analysts says a strong ridge of high pressure that has been camped over southwestern Idaho for much of the past 21/2 years is the single biggest factor causing the drought.

Idaho irrigators not only use tremendous quantities of water but also use outdated irrigation systems that allow water to evaporate quickly or leach through porous soils into groundwater.

Feeding off a water supply that is 11/2 times that of the Colorado River, Idaho irrigators use up to 20 acre-feet per acre each year to grow crops such as potatoes and sugar beets in desert soils.

Twenty acre-feet is enough water to cover an acre of cropland to the depth of one foot, 20 times.

That explains why Idaho, with a population of a million people, leads the nation in per-capita water use, ranks third in total water use and ranks second in use of water for irrigation.

Concerned that the South Fork of the Snake River's renowned trout fishery is at stake because of the drought, a coalition of sportsman and conservation groups has filed suit in U.S. District Court, seeking to block the government's plan to choke off downstream releases.

Named as defendants are Interior Secretary Donald Hodel and C. Dale Duvall, chief of the U.S. Bureau of Reclamation.