IDAHO FALLS, Idaho (AP) — Park officials in Yellowstone National Park report that efforts to protect threatened native cutthroat trout have progressed but that but concerns remain after officials discovered another invasive fish species.

Yellowstone fisheries biologist Todd Koel said officials first discovered a small cisco fish native to the Great Lakes two years ago.

Officials said it is unclear how the fish arrived in the park because the park has no natural connections to the lakes.

The discovery came as the park has made significant progress in suppressing invasive lake trout.

The trout population has declined more than 80% because of the efforts but officials now worry about the ciscos.

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10 Reasons NOT to Move to Wyoming

10 Reasons NOT to Move to Wyoming