EPHRATA, Wash. » A 65-foot-long crack in a Columbia River dam in central Washington has prompted officials to begin lowering the water level by 20 feet so inspectors can get a better idea of how serious the damage is.

Grant County Public Utility District spokesman Thomas Stredwick said Friday there’s no immediate threat to public safety from the crack in the Wanapum Dam, located just downstream from where Interstate 90 crosses the river.

Still, the Seattle Times reports Stredwick calls the crack a serious problem. An engineer earlier this week spotted a slight "bowing" above the spillway gates near where cars can drive across the dam. Divers found a 2-inch-wide crack along the base of one of the spillway piers.

Public utility district officials decided Friday that the failure risk was high enough that they should notify other government agencies and downstream water users.

Dam failure in the rural area would primarily affect farmers, fishermen and power generation. The dam can generate more than 1,000 megawatts of hydroelectric power.

Wanapum Dam was built in 1959 and is more than a mile long.