There is not a simple answer regarding dams and their impact on trout and salmon populations and fishing opportunities. It all depends on the type and operation of the dam itself. There are some 75,000 dams over six feet tall on rivers across the United States, and at least tens of thousands of smaller dams (possibly hundreds of thousands—the exact number is unknown). The cumulative impact of these structures can be devastating to rivers, trout and fishing.
TU does not advocate for the removal of all dams—in most cases, that is neither pragmatic nor appropriate. Many dams continue to provide important benefits such as hydropower generation, irrigation and flood control—as well as recreation and tail-water fisheries. In cases of functioning, economically viable hydropower dams, for example, Trout Unlimited volunteers and staff work with dam owners and regulatory agencies to provide more "fish friendly" operations.
Again, dams must be evaluated on a case-by-case basis. TU is committed to finding common-sense, pragmatic solutions to dam problems that degrade or destroy important fisheries habitat and impair angling opportunity.
Large dams that discharge water from the bottom of their impoundments (the water held back by the dam) often release clean, cold water that can be beneficial for trout populations downstream. Many large dams have "created" trout habitat in places where there previously was not trout habitat. These “tailwater fisheries” often are highly productive trout fisheries and several in the West (such as the Green in Utah, San Juan in New Mexico, Bighorn in Montana) are popular destinations for anglers.
It’s important for large dams to have adequate fish passage facilities, because healthy fish populations need to move to different areas of the river to satisfy different life-cycle needs, from food and shelter to reproduction. Salmon and other anadromous species migrate from the ocean, and dams significantly hinder their ability to reach their spawning grounds.
TU is working with federal, state and local partners on solutions to large dam problems. In the Northwest, we’re seeing increased momentum to remove and modify large dams that block salmon migration. After decades of work, TU helped secure the removal of two dams—the Elwha and Glines Canyon—on Washington’s Elwha River. Removing these two dams will open up over 70 miles of salmon and trout habitat that have been blocked for almost 100 years. Scientists predict that native salmon and steelhead populations will rebound from their current estimates of several thousand per year to over 300,000 in a matter of decades.
On the Penobscot River in Maine, plans to remove the lower two dams and bypass a third, along with enhanced fish passage on four other dams, will open up nearly 1,000 miles of habitat for endangered Atlantic salmon, sturgeon, river herring and other species of sea-run fish.
For salmon and steelhead anglers, these are dramatic and exciting victories, offering hope that salmon populations can rebound in the future, along with the fishing.
The majority of dams in the United States, however, are not large bottom-release dams. Tens of thousands of dams—most of them small concrete or earthen dams—fragment rivers and streams, block fish passage and significantly impair water quality. Many of them are aging and obsolete. The water impounded by these dams warms in the sun—often to a point where downstream reaches can no longer support trout populations (trout need clean, cold water to survive). The sheer number of these types of dams in rivers and streams across the country has had a serious impact on trout and salmon habitat, and, of course, fishing opportunity.
TU advocates for the removal of old, unsafe, uneconomical dams that are doing more harm than good. Selective small dam removal, thoughtfully carried out, is increasingly recognized as one of the most cost-effective fisheries and river restoration methods available..
For example, on Spread Creek in Wyoming, an important tributary of the Snake River, TU partnered with federal agencies to remove an aging concrete diversion dam that was no longer being used for irrigation. The project, featured in this TU video, opened more than 50 miles of upstream habitat to native Yellowstone cutthroat trout.
We’ve also completed scores of successful project that retrofit dams with fish ladders—another effective way to reconnect a watershed and give fish greater access to river habitat.