When do ecological restoration and huge quantities of dynamite go together?
That’s right—dam removal.
Some 90,000 dams plug America’s rivers, which is many more than conservationists want. Controversy has swirled around these American fixtures in the last few decades, and to understand why, we have to look back at their long history.
What are dams, exactly? Dams are barriers constructed across a stream or river that slow or stop its flow. They can be small—on the order of a few feet tall and wide—or tremendous: the Hoover Dam straddles the Nevada-Arizona border and is as long as four football fields.
Dams have been constructed for a variety of purposes. Some rivers were dammed to create a reservoir of clean water for human use, especially in the arid West. Others are used to generate hydroelectric power, a form of emission-free energy. Many, however, aren’t as useful. Some old dams were built to power mills that could grind corn, pull textiles, or saw lumber while also providing flood control. Sometimes dams were even created to supply a pond of clean ice that could be extracted for storing food safely. In short, many dams were built for purposes that are obsolete in today’s world—but the dams are still there.
What’s wrong with that? Ecologically, the problem with dams is that they bring the river or stream system to a standstill. Sediments and nutrients that previously flowed through the river are slowed or completely stopped, oversaturating the reservoir and starving the rest of the river. The river slows and warms up, and the newly formed reservoir upstream can take on the ecology of a lake. This can cause all kinds of mayhem: toxic algae blooms in the reservoir are one possibility, and temperature changes throw off all the aquatic organisms that adapted to live there before the dam.
Plants and animals are also blocked from their original habitat. For migratory fish species, this can be devastating—as it has been for salmon. These famous migratory swimmers swim upstream in huge numbers every year, returning to their own birthplace to spawn, and building a dam essentially shuts down their life cycle. Adults can’t reach the spawning ground or hatchlings can’t migrate to the ocean. The dams across Washington’s Elwha River cut the river’s salmon population from 400,000 fish per year in the early 1900s to 3,000.
Ecologists and conservationists aren’t the only ones who want the dams gone. Native Americans are often big proponents of dam removal too: The Lower Elwha Klallam Tribe led the movement to remove the Elwha dams. Salmon is essential to their food supply and their culture, and the tribe had a legal right to half of all the river’s salmon catch.
Considering the disruption dams cause to river ecosystems, potentially valuable species, and Native cultures, removal has become a hot topic. As an ecological restoration tool, it can be incredibly effective—all you need to do is get rid of the dam, and the river takes care of the rest of the ecosystem. Even better, the river often takes care of it more quickly than scientists anticipated.
Chunk by concrete chunk, the biggest dam removal project in history was completed in 2014 when the dams on the Elwha all came down. No one knew how long it would take the built-up sediment from the reservoir to make its way through the river. Explained one oceanographer, “We didn’t know if that would take two years or two months.” It took two weeks. And the same year that the river was freed, for the first time in a century, all five species of salmon returned.
Considering the potential gains to be made by removing old dams, it’s imperative that we evaluate each and every dam in the U.S. and whether it really needs to be there. Some dams do provide valuable, fossil-fuel-free energy, but not as many as you might guess: only 3% of dams in the US produce hydropower, accounting for just 7% of our total energy demand. Even if all those are left alone, what of the other 97%?
The first priority should be removing dams that are totally obsolete. And there’s no shortage of those: according to the EPA, a staggering 75-90% of American dams no longer serve any functional purpose. Let that sink in: the vast majority of stress and change to river ecology, blocking valuable fish species from their habitat, and disrupting indigenous cultures… is totally useless. Obsolete dams have plugged our rivers for far too long; now, what are we waiting for?
What You Can Do
- Follow and support the efforts of American Rivers, a nonprofit dedicated to dam removal and upgrade
- Seek out and support dam removal processes in your own state and neighborhood; the Massachusetts Division of Ecological Restoration provides funding and technical support for private dam removal projects