Plans to raise Arrowrock Dam by more than 70 feet don’t pencil out, the Army Corps of Engineers told a stunned Idaho Water Resources Board on Wednesday, reports Rocky Barker of the Idaho Statesman. The Corps conducted a feasibility study, funded by a $1.5 million payment from the state of Idaho, which favors the project, and determined that the cost of raising the dam would exceed the benefits. Raising Arrowrock would cost $1.3 billion.

The U.S. Bureau of Reclamation presented a separate proposal to raise the larger Anderson Ranch Dam upstream on the South Fork of the Boise River, after the Corps said it would not move forward with raising Arrowrock, Barker reports.

The water board is in charge of planning future water uses and supplies for the state, and provides bonding and other financing for water projects. The Army Corps and the Bureau of Reclamation jointly operate the Boise River dams and major diversions; the Corps has Lucky Peak while the bureau has Arrowrock, Anderson Ranch and Lake Lowell. Barker’s full report is online here.