Lake trout have turned up in the Swan Valley's Lindbergh Lake, presenting a new threat to the drainage's population of native bull trout.

Montana Fish, Wildlife and Parks recently conducted spring gill netting in Lindbergh Lake, catching four lake trout ranging from 16 to 19 inches long.

While there have been reports of anglers catching non-native lake trout, it was the first confirmation of the species in Lindbergh Lake.

"It's not totally unexpected but it's very disappointing," said Jim Vashro, the state's regional fisheries manager.

The fish are likely migrants from Swan Lake, some 40 miles down the Swan River.

Because there were three reports of anglers catching lake trout in weeks leading up to the netting, that is an indicator that the species may be abundant in Lindbergh Lake.

The same netting turned up 10 bull trout, but the catch of four lake trout doesn't necessarily reflect the relative abundance of the two species, which are top-end, competing predators.

"We'll get back in there and do some more work to determine relative abundance and we'll be really be looking at where reproduction is occurring," said Vashro.

He added that a lake trout population that is reproducing in Lindbergh Lake "poses a lot more potential for harm."

One characteristic of the lake - the absence of mysis shrimp - will not help lake trout, which tend to have much better juvenile survival when the shrimp are present.

Vashro said there is concern that lake trout will continue to proliferate in the Swan River drainage. So far, lake trout have yet to be detected in other waters, such as Holland Lake.