See article from local paper, also similar news from the YNP website. This is nothing new the past few years, though this year the (ought to be mandatory) closures are more extensive than they have been in the past.

Heat killing fish in Yellowstone
YELLOWSTONE NATIONAL PARK, Wyo. - A heat wave has warmed the Firehole River to as much as 82 degrees, killing hundreds of rainbow and brown trout.

Park officials noticed the kill Friday. Yellowstone spokesman Al Nash said temperatures above 73 degrees can be stressful or even fatal for trout.

He said the trout died within the previous three days.

Meanwhile, park officials enacted voluntary fishing closures at several areas because of the stress that warm water places on fish.

"We have a strong, involved, responsive user group here," said Nash. "We know that people come here because of the world-class fishing opportunities. We know how important it is to them and we know they'll join us in protecting this resource."

He said the current advisory is earlier and more widespread than in years past.

"I am not aware that we've involved this many rivers and creeks before," he said.

In northern Yellowstone, the advisory applies to the Gardner River below Osprey Falls; Lava Creek below Undine Falls; Lamar River below Cache Creek; all of Slough Creek; Soda Creek below Amphitheater Creek; and Yellowstone River below Seven Mile Hole.

On the west side of the park, the advisory applies to the Madison River, the Firehole River and to the Gibbon River below Gibbon Falls.

In southern Yellowstone, the advisory covers the Bechler River below Ouzel Creek; Fall River below Rainbow Falls; Mountain Ash Creek below Union Falls; Proposition Creek; Boundary Creek below Dunanda Falls; Robinson Creek; and the Snake River below Six Mile Ford.

Information from: Jackson Hole News & Guide, http://www.jhnewsandguide.com

A service of the Associated Press(AP)