River levels are dropping rapidly as summer temperatures continue to climb, and both trends spell trouble for Montana’s trout. As Montana Fish, Wildlife & Parks prepares for fishing closures, anglers can do some things to help fish out.

By Saturday, high temperatures are predicted to top 100 degrees and stay that way at least through Wednesday for parts of western Montana. That’s 20 to 25 degrees above normal for this time of year and the extended heat wave will break records, according to the National Weather Service. It's a preview of what summers may become due to climate change.

Even worse, the nighttime lows are predicted to barely sink into the 60s, so there won’t be much relief.

While some Montanans can escape to air-conditioned houses, wildlife that aren’t adapted to such hot weather are in for a miserable week.

That is especially the case for trout and other aquatic animals, because stream levels are plummeting after not rising much to begin with this spring. Shallow rivers heat up much faster than deep ones, so water temperatures could climb to levels that are deadly for trout.

The U.S. Geological Survey reports that streams in much of western Montana – north from Ravalli and Granite counties and east to the Continental Divide – are in moderate to extreme drought conditions.

For example, the Bitterroot River and the North Fork of the Sun River are running at 30 percent of where they should be at the end of June. The Clark Fork and Blackfoot rivers near Missoula aren’t doing much better.

The water temperature at the mouth of the Blackfoot has peaked above 62 degrees for the past several days, and some days have touched 64 degrees.

While nonnative fish such as rainbow and brown trout can tolerate higher temperatures, Montana’s native trout will suffer the most.

Biologists have identified 67 degrees as a lethal high temperature for westslope cutthroat trout while rainbow trout can tolerate up to 75 degrees. However, trout don't die the minute the water heats to those levels - most fish have to live at those temperatures for days to die.

If fish are stressed by fishing, they can die at lower temperatures.

Studies estimate that stress causes between 10 and 30 percent of trout die after being released, depending on conditions and how the fish are handled.

FWP policy is to shut a stream to fishing if flows are low and the water temperature reaches or exceeds 73 degrees for three days in a row. Water temperatures cycle over a day, reaching the highest temperatures in the afternoon.

In May, the FWP commission was already anticipating having to close rivers after hearing a dire streamflow summary from fisheries administrator Bruce Rich.

“Right now, things are looking between tough and grim as far as our water situation this year,” Rich said. “We’re going to be at the mercy of the summer weather, and if it’s hot and dry, it’s going to be a very tough summer for us.”

As streams get warmer, anglers should remember that fish will be stressed more easily. so they should do a few things to help trout out:

-       fish during cooler times of the day

-       don’t “play” the fish once they’re on the line

-       try to keep the fish quiet and in the water while releasing it.

Anglers often like to take photographs of themselves with their fish. But if the fish isn't being kept for dinner, best to take photos holding the fish in the water.

Even without high water temperatures, biologists have found that trout that are kept out of water for even a few seconds can die after being released.

A 1992 Canadian study on rainbow trout discovered that every second counts. Fish that were “played” but then released in the water had a survival rate of 88 percent. But if they were held out of the water for 30 seconds, the survival rate dropped to 62 percent. If exposed to the air for a minute, less than a third of the trout survived.

So do the fish a favor, especially during the heat wave: take selfies of yourself with a cold drink instead.