Biologists who want to know what types of fish live in the Tennessee Valley Authority lakes have an uncanny technique for uncovering what lurks beneath the surface. The method involves researchers putting a generator in the water that releases an electrical charge to shock the fish into a “zombie-like” state.

Fittingly known as “electrofishing,” the technique renders the fish momentarily incapacitated and causes them to rise to the surface. Biologists can then scoop the stunned fish up with a net, jot down what they observe, and then plop the “zombie bass” back into the lake once they’ve begun to revive.

“By looking at the overall health and condition of the fish we collect, we can tell a lot about what’s going on with the fishery,” John Justice, a iologist with the Tennessee Valley Authority, told Associated Press.

According to AP, the lakes in the Tennessee Valley Authority, a federally-owned U.S. corporation that covers most of Tennessee, parts of Alabama, Mississippi and Kentucky, and small areas in Georgia, North Carolina and Virginia, are some of the most biologically diverse in North America. Data collected through electrofishing helps biologists determine how to best manage the lakes. Researchers use the information to establish catch limits, water levels and stocking programs.

Electrofishing is a fairly common scientific survey method and is used to sample fish populations for density and species composition. Rarely are the fish injured during the surveys.

“This method of collecting fish can be one of the best methods for nonlethal collections of resident fish species, allowing the scientist to temporarily collect organisms and retain them in an aerated holding tank until the right number, size, sex, or species have been collected,” the U.S. Environmental Protection Agency notes.