FISH-FRIENDLY PASSAGES
Removing the Barriers to Conservation Unexpected partners are collaborating to unclog our rivers for people and fish
When you think of a fish passage, maybe you picture salmon leaping up ascending pools of manmade fish ladders laid over dams in the western United States. Some salmon and trout species can clear 6-foot waterfalls to reach the headwaters where they hatched and will return after years at sea. Think of the photos and videos of grizzly bears catching huge fish mid-air as they migrate upstream. Impressive, but even salmon cannot leap the towering dams on the rivers where they spawn. That has been a problem people have tried to solve for years, hence the feats of engineering such as fish ladders and other fish passage projects.
Missouri does not have salmon swimming in from the ocean, but we do have other species of fish that migrate seasonally. We also have threatened and endangered species of mussels, snails and other aquatic organisms. Many can be found in only a few streams in the Interior Highlands region that spans much of Missouri and Arkansas into Oklahoma, and many of these streams have been chopped up by aquatic barriers big and small. It doesn’t take a 50-foot dam to halt a mussel’s movement. A low-head dam that barely breaks the water’s surface or a concrete slab for vehicles to cross the stream is impassable for small fish and other freshwater animals.
The Interior Highlands, including the Missouri Ozarks, is full of these barriers. You may have noticed that many such road crossings have round culvert pipes to allow water, and presumably fish, to pass through. But look closely. When the creek rises, the pipes turn a stream’s flow into jets, like putting your thumb over the mouth of a garden hose. Over time, that jet will carve a pool into the stream bed. Under the right conditions, those pools expand, making that culvert into a 3-foot tall waterfall, too high for our small freshwater animals to navigate. These crossings threaten already- struggling species. The Niangua darter
12 MISSOURI : ACTION AND IMPACT
THIS PAGE A crew replaces a crossing in Missouri with a fish-friendly bridge. © Rob Pulliam/TNC
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