YELLOWSTONE NATIONAL PARK, Wyo. (AP) — Workers at Yellowstone National Park intend to poison non-native brook trout on a stream system in the park so it can be restocked with native cutthroat trout.

Starting on Monday, Sept. 23, biologists at the park will introduce a fish toxin to Elk Creek and its tributaries to remove brook trout. The project won't affect the nearby Yellowstone River.

Biologists will then reintroduce cutthroat trout.

The park is advising visitors not to swim in or drink water from the streams from Sept. 23 through Sept. 30. Workers will post warning signs at affected areas.