Nonnative Fish Species


Nonnative Fish Species

Nonnative fish distribution and their influence on native fish are not static. While they have not been intentionally stocked since the 1930s, nonnative fish continue to advance into new habitats and hybridize with or displace native fish.

Hybridization of cutthroat trout resulting from rainbow trout range expansion continues to be the greatest threat to the park’s remaining native fish populations in waters outside the Yellowstone River headwaters, Yellowstone Lake, and the Snake River headwaters.

Not all movement by nonnative fish in Yellowstone has occurred naturally. Nonnative lake trout, intentionally introduced by managers in 1890 to Lewis and Shoshone lakes, and introduced to Yellowstone Lake (by unknown means) in the mid-1980s, first appeared in angler catches in 1994. The lake trout population expanded and, over the following decade, caused a rapid decline in the Yellowstone cutthroat trout (YCT) population in Yellowstone Lake. Currently the NPS and contracted gill netters remove approximately 300,000 lake trout from Yellowstone Lake annually.

Underwater photo of white-spotted lake trout
Lake Trout

Lake trout prey on Yellowstone cutthroat trout.

Rainbow trout in the hands of an angler
Rainbow Trout

Rainbow trout are native to North America in waters which drain to the Pacific Ocean from northern Mexico to Alaska.

Eastern brook trout swimming
Eastern Brook Trout

Eastern brook trout was the first nonnative species introduced in Yellowstone—stocked in the (then fishless) Firehole River in 1889.

Head and body of a brown trout laying on the ground
Brown Trout

The brown trout is the only nonnative fish species in Yellowstone that is not native to North America.

Lake chub held in hand
Lake Chub

Native to the Missouri and Yellowstone river drainages in Montana and Wyoming, the lake chub is not native to Yellowstone National Park.


Source: Data Store Collection 7797. To search for additional information, visit the Data Store.

Two shells sit on a dime and are about the same height as the coin
New Zealand Mud Snails

New Zealand mudsnails are invasive and have a significant detrimental effect on Yellowstone.

Two speckled fish with black tails swim in a colorful streambed
Whirling Disease

Whirling disease can infect some trout and salmon.

Brightly-clothed people in a river near a steaming thermal feature
Red-rimmed Melania

Red-rimmed melania, a small snail, was discovered in a warm swimming area.

Angler fishing in Yellowstone during a golden morning.
Catch a Fish

Be a responsible angler and understand the regulations before you come.

Photo of a park employee cleaning a boat with a power washer.
Clean, Drain, and Dry

Protect park waters by preventing the spread of aquatic invasive species.

A young bison calf with rust-red fur.

Learn about the park's abundant and diverse species—67 mammals, 330 birds, 16 fish, 5 amphibians, and 6 reptiles.

Last updated: May 8, 2023

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PO Box 168
Yellowstone National Park, WY 82190-0168



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