In Lake Roosevelt, over one million rainbow trout and kokanee are raised in hatcheries and net pens each year. Fish in net pens are generally released around the end of May, which is when they are large and strong enough to survive on their own.

The net pens float on the surface of the water. Within the net pen, fish travel anywhere from the surface to a depth of up to fourteen feet (4.3 meters). Being held in this small area means they are particularly vulnerable to TDG supersaturation.