Huge rainbow trout pigging out in Clearwater’s North Fork

There are some huge fish lurking in the North Fork Clearwater River below Dworshak Dam, and they aren’t steelhead or salmon.

A few anglers have hooked into absurdly fat rainbow trout that apparently feed on kokanee salmon that are occasionally flushed through the dam. Aaron Marshall of Boise hooked one in July, an Idaho Fish and Game biologist saw one caught in June and a fish of similar size was found dead above the dam earlier in the year.

Marshall figures the fish he caught and released weighed 22 to 25 pounds.

“I thought, ‘Wow, I caught myself a baby beluga.’ I’ve never seen any fish like that, ever,” he said. “It was a fighter. It was just a big, old, fat trout.”

Not sure what the fish was, he returned it to the water. Under Idaho fishing regulations, any rainbow trout more than 20 inches long caught from the Clearwater River, its North Fork below the dam, or any other river where the fish has the ability to migrate to the ocean is legally defined as a steelhead. By that definition, Marshall’s fish could only be kept during an open catch-and-kill steelhead season. However, his fish had an intact adipose fin, meaning it would qualify as a wild steelhead and would never be available to harvest.

But nobody thinks the fish was actually a steelhead. It’s much too fat and its head and snout are too short. Don Whitney, a fisheries biologist for the Idaho Department of Fish and Game, said the fish is likely a resident rainbow. He said it could be a descendant from a strain of kamloops trout the department used to release in the Clearwater. When the now-defunct program first started, the kamloops planted in the river were not sterile. Whitney said the fish could be an offspring of one of those fish. In later years, the fish were sterilized.

“I would expect that is either one of our old kamloops that was successful in reproduction or it’s just a resident rainbow that has found a great feeding method off of those kokanee,” he said. “Some of those big pigs like that are just hanging out there gobbling kokanee.”

Feeding on either live or dead kokanee flushed through the dam would offer trout a high-protein, high-fat diet. Whitney was fishing below the dam in June when he saw another fishermen land a fish similar to the one Marshall caught. He helped the angler land and release it.

“That looks pretty damn close to what I put my hands on,” he said. “It’s definitely not the same fish but it’s really close.”

He said a survey crew from the Idaho Department of Environmental Quality found a dead rainbow that was about 30 inches long floating just upstream of the dam. It also had a fat belly.

Whatever the source of the fish, Whitney said it’s impressive.

“What an awesome fish,” he said.