Sep. 13--The region's prolonged drought is drying up one of the state's cleanest energy sources: water.

Receding water levels are forcing Progress Energy and Duke Energy to cut back production of hydroelectric power. Progress Energy's production is down nearly 30 percent at its three hydroelectric plants in the state. Duke Energy's 18 plants in the state has fallen 45 percent compared with this time last year. "Production is down probably more than it's ever been down before," said Cecil Gurganus, hydro plant manager for Raleigh-based Progress Energy. Because hydroelectric power represents only about 1 percent of the total electricity produced in the state, both companies say the cutbacks haven't had a substantial effect on power supplies.

But they have had to tap other energy sources. "We have to make it up somewhere," said George Galleher, Duke Energy's senior engineer for hydro operations. "What it means is we either have to go out and buy [the electricity] or we have to burn more [natural] gas in combustion turbines." The hot weather is also affecting operations at conventional power plants that rely on water for cooling. Charlotte-based Duke shut down its Riverbend Steam Station for a half-day last month because the coal-burning plant outside Charlotte would otherwi e have exceeded environmental temperature limits on outflow water that is released into the river.

Progress also is monitoring falling water levels at Harris Lake, the primary source of cooling water for the Shearon Harris nuclear plant in Wake County. The man-made reservoir is approaching record low levels, but the drought poses no immediate concern for the nuclear plant, company officials say. Water is one of North Carolina's oldest energy sources, dating to the birth of the state's electric utilities in the late 1800s. Because water currents don't require burning fossil fuels that emit greenhouse gases, hydroelectric power counts as a renewa le resource. But water is renewable only as long as the rivers don't run dry.

The state is experiencing one of the most severe droughts in recent history, and rainfall in the Triangle is 10 to 15 inches below normal for the year. At hydroelectric stations, less water means that less electricity is produced. A hydroelectric plant generates electricity on the same principle as any other power plant, except the energy source that drives the turbines comes from water current instead of pressurized steam. The water collects at a dam and then is channeled to a h droelectric generating station nearby, spinning the turbines up to 10 revolutions per second. As waterways shrink, more time is required to fill the dams, resulting in fewer water releases to drive the turbines.

The hydroelectric cutbacks affect more than electricity generation. The water releases affect river flow and can be both a bane and boon for outdoors enthusiasts. Reduced water releases limit the number of days for rafting, kayaking and canoeing. The state's hydroelectric plants have been a salvation for outdoorsmen who seek the rapid currents. Many natural rivers are so dry that they are unsuitable for advanced paddling, said Larry Ausley of Apex, who is president of the Carolina Canoe Club. "The dammed rivers are our options right now, and that's where people are going," he said. "Just this week I've run into friends from Georgia, South Carolina and Tennessee on the Nantahala River, because they just don't have anywhere else to paddle." Along depleted waterways, some Duke hydroelectric plants have cut back production as much 75 percent, Galleher said.

Progress Energy's experience is similar. Last month, Progress' Walters Plant on the Pigeon River in Haywood County on the Tennessee border was scheduled to release water four times a week, not only to generate power but to accommodate whitewater rafters The water shortage reduced the scheduled water releases to once a week. How soon the releases will return to normal is unclear. The hydroelectric water reservoirs are fed by numerous rivers and tributaries in the state, some more seriously affected by the drought than others. In general, the drought is more severe in Western North Carolina than in the Triangle.

Subject to the whims of the weather, hydroelectric operators can only guess when they will be back to full power. "There's really not a lot of guidelines on this," said Duke's Galleher. Staff writer John Murawski can be reached at 829-8932 or john.murawski@newsobserver.com .