Workers were racing to beat a thaw in the weather and clear a blockage at an earthen dam that threatens to break and flood about 25 homes and businesses, officials said.

Workers were trying to clear a drainage pipe blocked by beavers at the 7.5-million gallon reservoir near the mountain town of Oakland before a thaw that was expected to begin Thursday and continue through the weekend.

"If it warms up to 50 and rains - and we already have several feet of snow - there could be a pretty rapid runoff. And if you have that type of runoff there, it could weaken the dam," said Asa McCain, mayor of the town of 1,900.

Workers were struggling to move two tractor-trailer-size pumps through at least 10 inches of fresh snow to start lowering the 22-foot water level, said Katie Leahan, state emergency management spokeswoman. Each pump can move 2,000 gallons of water per minute, possibly enabling divers to reach the drainage system, she said.

Six divers were flown in to Oakland on Tuesday night. The divers, working for two hours in the dark, could not clear an obstruction made by beavers, Leahan said.

The dam, part of a flood-control system built in 1964, is on the grounds of Garrett County Memorial Hospital, which is uphill from the reservoir.