The lakes in question don’t have many fish in them, but they’re very popular for fishing. Every year, Utah stocks them with fish specifically raised for fishing. These fish are often sterile, allowing for population control and preventing them from affecting the native fish populations. The species added include rainbow trout, cutthroat trout, brook trout, tiger trout, splake and Arctic grayling, and they’re usually only about 1 to 3 inches long when they’re dropped off.
And don’t worry about the safety of the fish as they fall from the planes — it’s actually a very safe way to do it and is less traumatizing than other methods. Post-drop surveys have also found that the survival rate for the fish is much higher than when they are brought in on dirt bikes or backpacks, or horse-drawn milk cans as was done before the 1950s. “Because the fish are small and released along with water, they easily survive their airplane drop without injury,” DWR said. “They fall a bit like leaves.”