Starting Wednesday, park officials will prohibit fishing on the Gibbon River below Gibbon Falls, Firehole River below Keppler Cascades, and the Madison River.
The reason is water temperatures ranging into the high 70s — too warm for trout. Warm weather, hot water from thermal features and low stream flows all are causing the water to warm up.
Warm water can be stressful or even fatal for trout.
Yellowstone officials say the forecast calls for more warm weather and that could cause additional areas to be closed to fishing.