PIERRE, S.D. (AP) - Drought-drained Lake Oahe has hit an all-time low, about 32 feet below normal, the Army Corps of Engineers says.

The lake level dropped to 1,571.96 feet below sea level Monday. The old mark, set in 2004, was 1572 feet.

However, Oahe is still the largest lake in South Dakota, and walleye fishing there has been good this year.

Oahe could fall another 6 inches by month's end, but it is expected to rise by 1.5 feet in September, said Eric Stasch of the Corps of Engineers.

The corps has released water from North Dakota's Lake Sakakawea to try to help Oahe, but officials said earlier it did little good. Lake Sakakawea also is headed for a record low.

With the water level low, power generation also is dropping. That means power suppliers, cooperatives and cities that depend on the Oahe Dam for electricity are looking elsewhere to find enough to meet demands.

The Western Area Power Administration, which sells the electricity generated by Oahe, has been forced to buy power from other generators so it can supply all its customers.

Greg Vaselaar, a WAPA field representative from Huron, said the federal agency reportedly spent about $2.7 million in July to buy electricity to meet customers' requirements.

WAPA has a rate increase scheduled for January, but the cost of having to compensate for a 40 percent loss in electricity from Oahe likely will mean another increase later, Vaselaar said.

"Well, we had a 12 percent rate increase Jan. 1 (2006) and there will be another 6 percent increase on Jan. 1, 2007 - that's a given," Vaselaar said. "It's all tied to the drought situation we've been in for the last few years.

"Now we're looking at 2008. We have to go through a (public hearing) process, but, yeah, it's going to be a significant increase - probably larger than the 18 percent we've already planned."

WAPA provides electric power to a number of electric cooperatives, state government, Ellsworth Air Force Base and 33 towns and cities in South Dakota.

Watertown gets about one-third of its electricity through WAPA. No communities get all their power from WAPA, Vaselaar said.

The cost of power is high, he said.

"It's not unusual for us to have to buy power," Vaselaar said. "But now the cost differential is so much greater now. It's almost three times what it was in the late 80s and early 90s.

"We've never seen the market this high."

Although WAPA is raising rates, that's a cost of doing business with a federal agency that has supplied communities with inexpensive electric power for decades, said Geoff Heig, municipal utilities general manager in Watertown.