The Lake Cumberland reservoir is 101 miles long in length and has 1,255 miles of shoreline, providing a total storage capacity of 6,089,000 acre-feet (1 acre-foot = 1 acre, 1 foot deep or 325,850 gallons).  The upper portion of the reservoir containing 2,094,000 acre-feet of area, is used to hold floodwaters which would otherwise cause flooding downstream.  Such impounded water is utilized to the maximum extent possible for power production and the surplus water is released through the spillway gates after any flood danger had passed.

Of the remaining 3,995,000 acre-feet of reservoir capacity, 2,142,000 acre-feet, corresponding to a drawdown of 50 feet, is allocated specifically for power operation, leaving a minimum pool of at least 1,853,000 acre-feet available at all times for public use and conservation purposes.  The electrical energy produced by the project is sufficient to supply the needs of an average city with a population of 375,000.  Incidental to the production of power, the water released through the turbines provides a favorable streamflow below the dam.  In supplementing low flows, this water improves domestic water supply, reduces stream pollution and provides aid to navigation.

The reservoir normally fluctuates between 50,250 acres at the top of the power pool and a minimum surface area of 35,820 acres.  During periods of high inflow, when it is necessary to utilize the floor storage, the surface area may reach 63,530 acres.  However, such floods occur infrequently, and the levels resulting from minor floods and power operations do not seriously interfere with most recreational activities.