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Where the Big Fish Swim

July 22, 2011 | by Bruce Auchly

Dave Yerk of Choteau holds a rainbow
trout caught fly fishing in a central
Montana reservoir. Photo by FWP.

After what seems like forever to get here, summer has arrived. Streams and rivers are clearing, and fishing is improving. Now it’s just a matter of where to go.

For weeks, most rivers and streams were high and muddy. That forced anglers to hit lakes and reservoirs. Those who did often found good fishing.

Montana’s impoundments east of the Continental Divide have the ability to grow trout. Big ones and fast.

Take a deep coulee and dam it up. Wait for water to fill it, which is not a problem in this the year of the wet, add rainbow trout and stand back.

Central and eastern Montana’s advantage lies in its rich soil and dry weather. In wet climates, rain over eons of time can wash all the nutrients out of the soil. Not so here, where a prehistoric sea deposited thick layers of sediment.

When the sea dried up, the sediment turned to sedimentary rock, trapping nutrients such as potassium, calcium, magnesium, and phosphate.

Over time weather and climate broke that rock into soil. Then, about 75 million years ago, the rise of the Rocky Mountains left our soil in a dry rain shadow, preventing the nutrients from leaching out.

Central and eastern Montana may look like a wasteland to the untrained eye, but just add a little water and almost anything will grow. The soil holds a wealth of natural fertilizer and nourishment ready to go into any plant.

When bison roamed the prairies they grew fat eating nutritious grass. And the state’s wheat commands a high price because it has a high protein content.

As for fish, the combination of water, soil and summer sun provides the perfect growing conditions for aquatic vegetation, which attracts lots and lots of insects: damselflies, leeches, water boatmen and tiny freshwater shrimp, called scuds.

A good example of how fast and fat trout can grow eating those aquatic insects are the lakes on the Blackfeet Indian Reservation.

The reservation stocks about two dozen lakes each year. The rainbow trout average 5 inches long when planted. In one year they can grow a remarkable 7 to 8 inches. That’s part of the reason thousands of non-tribal anglers fish the reservation each year.

The reservation lakes don’t have a lock on a trophy trout fishery. It can happen almost anywhere on the prairie east of the Rockies as long as there are periodic trout stockings.

Rainbow trout need a good flowing stream with gravel beds for spawning. That’s something ponds usually lack. So regular stockings are required.

Problems arise when people put other fish like minnows or yellow perch in a pond full of rainbows. Those other species can spawn in ponds and end up out competing trout.

Usually the reasons people stock other fish are to provide food for the trout or give anglers another game fish to catch. Both reasons are mistaken and can really mess up a fantastic rainbow fishery. But that’s a subject for another day.

Now, it’s fishing season. Finally.