Cycles of Dependency: Salmon and Macroinvertebrates in the Columbia River Basin

A NWNL NextGen Blog by Johanna Mitra, Stony Brook University.

All Photos © Alison M. Jones.

This is the latest post to our NWNL NEXTGEN BLOG series. Since 2007, NWNL has supported watershed education with college internships and blogging opportunities. Our NWNL NEXTGEN BLOG series posts only student essays; sponsors a forum for its student contributors; and invites student proposals to write on watershed values, threats and solutions.

Johanna Mitra is currently an undergraduate student at Stony Brook University. She is majoring in ecosystems and human impact with a focus on wildlife conservation and minoring in geospatial science. This is the second in a series of blogs about the importance of macroinvertebrates in aquatic ecosystems. Read part-one on macroinvertebrates in the Mississippi River Basin.

My previous blog explained how critical aquatic macroinvertebrates are to the bodies of water they inhabit. Macroinvertebrates serve as food for other species and play a vital part in the water-nutrient cycle. These small, spineless and often under-appreciated species help maintain water quality in streams, lakes and rivers across the world. The Pacific Northwest’s Columbia River Basin is no exception. Its 1,200 miles of river are home to mayflies, mussels, dragonflies, snails and many more species that spend a portion or all of their life in the water.

Most people associate the Columbia River Basin with its abundance of salmon, rather than its numerous macroinvertebrates. Indeed, historically the Columbia River produced up to 16 million salmon every year -including Chinook, coho, sockeye and steelhead salmon.[mfn]Columbia River Inter-Tribal Fish Commission[/mfn] Their numbers have decreased significantly over time due to the numerous dams built across the river, climate change and declining water quality.[mfn]American Rivers[/mfn]

Grand Coulee Dam and Lake Roosevelt

Before dams, the cool waters and strong flow the river basin’s streams allowed for the proliferation of salmon. Not so coincidentally, these same conditions also allowed macroinvertebrates to thrive and function as a key food source for young salmon before their migratation to the ocean as adults.[mfn]World Salmon Council[/mfn] In sharing the same ecosystem and sensitivities to habitat changes, aquatic macroinvertebrates and salmon act jointly as important indicators of water quality.

Chinook salmon In Washington State

How Dams Shaped the Columbia River

Today, Columbia River hydroelectric plants account for about 44% of the total US hydroelectric generation.[mfn]Lillis, Kevin[/mfn] There are over 400 dams on the Columbia and it’s tributaries.[mfn]Vintinner, Erin[/mfn] Millions of people in the Pacific Northwest rely on these dams for electricity, drinking water and irrigation of over 600,000 acres of farmland.[mfn]American Rivers[/mfn] Per the 1964 Columbia River Treaty, ratified by the US and Canada, these dams also provide significant flood protection due to three storage dams in Canada that collect runoff as well as providing additional power.[mfn]Lillis, Kevin[/mfn] However, this cascade of dams fundamentally alters the flow of the river and comes at a heavy cost to the surrounding environment.

Revelstoke Dam on Canada’s Columbia River

Threats to Salmon & Macroinvertebrates

Studies show that healthy macroinvertebrate communities occur where there are healthy populations of spawning and young salmon. Correspondingly, salmon numbers dwindle in areas with poorer conditions and fewer macroinvertebrates .[mfn]Plotnikoff, Robert W. and Joanne Polayes[/mfn] This co-dependency illustrates the snowball effect that dams have on river ecosystems.

Salmon at Rocky Reach Dam on the Columbia River

A salmon’s life cycle begins in freshwater streams where it relies on macroinvertebrates for food in shaded streams with high levels of dissolved oxygen and cold water. After a few months to a year, “cues” prompt the young salmon to migrate downstream. They next inhabit the brackish waters of the Columbia River Estuary before transitioning to the open ocean for up to eight years. Salmon conclude their life cycle by returning upriver to the streams in which they were born to spawn and die.[mfn]National Park Service[/mfn] Typical of many of nature’s cycles, the streams’ macroinvertebrates eat the decaying salmon carcasses, thus restoring the water’s nutrients and nourishing yet another generation of salmon. [mfn]White, Seth[/mfn]

The salmon’s life cycle depends on their ability to migrate up and downstream, unimpeded by dams or water diversions. Some dams offer passage via fish ladders, but many do not. The dams also reduce stream flow and raise water temperatures – a double threat to young salmon.[mfn]World Salmon Council[/mfn] While the more sedentary macroinvertebrates don’t need to cross dams, they are affected by dams. Macroinvertebrate communities have difficulty establishing themselves in areas where natural flow patterns have been altered; and their sensitivity to fluctuating temperatures makes it harder for them to survive.[mfn]White, Seth[/mfn] This dam-induced reduction in macroinvertebrate numbers in turn affects the healthy of salmon numbers.

The Future of Dams in the Columbia River

Building dams is a massive undertaking. As their efficiency reduces over time, the cost of maintenance outweighs the services they provide. Many dams in the Pacific Northwest, are outdated, no longer serve a functional purpose, and are unsafe.[mfn]Cho, Renee[/mfn] In response, numerous organizations have created initiatives to remove such dams and thus restore river habitats for salmon and microinvertebrates. Local communities, energy companies and the federal government are all involved in efforts to open up waterways for fish migration and return wetlands, estuaries, and river tributaries back to their original state. For instance, there are ongoing efforts along the Columbia’s Main tributary by Save Our Wild Salmon and American Rivers to remove four costly and ineffective dams from the Lower Snake River. Those dam removals would allow endangered salmon access to 5,500 miles of protected river habitat without loss to electrical supply or transportation access.[mfn]Save Our Wild Salmon[/mfn] The last 50 years have seen the removal of more than 600 dams across the United States. Such progress increases the chances of healthy salmon and macroinvertebrate populations to the Columbia River Basin.

The Columbia River and Mount Iconoclast


Cho, Renee. “Removing Dams and Restoring Rivers.” Earth Institute of Columbia University, August 29th, 2011. Accessed on June 21, 2020 by JM.

“Columbia River.” American Rivers, n.d. Accessed on June 19, 2020 by JM.

“Columbia Basin Salmonids.” Columbia River Inter-Tribal Fish Commission, n.d. Accessed on June 19, 2020 by JM.,and%20less%20than%201%25%20chum.

“Introduction to Salmon Biology.” World Salmon Council, n.d. Accessed on June 19, 2020 by JM.

Lillis, Kevin. “The Columbia River Basin provides more than 40% of total U.S. hydroelectric generation.” U.S. Energy Information Administration, June 27, 2014. Accessed on June 19, 2020 by JM.

Plotnikoff, Robert W. and Joanne Polayes. “The Relationship Between Stream Macroinvertebrates and Salmon in the Quilceda/Allen Drainage.” Washington State Department of Ecology, March 1999. Accessed on June 21, 2020 by JM.

“Restoring the Lower Snake River.” Save Our Wild Salmon, n.d. Accessed on June 21, 2020 by JM.

“The Salmon Life Cycle.” National Park Service, n.d. Accessed on June 21, 2020 by JM.

Vintinner, Erin. “General Characteristics of the Columbia River Basin.” No Water No Life, n.d. Accessed on June 19, 2020 by JM.

White, Seth, et al. “Conservation Planning for Climate Change Impacts to Benthic Macroinvertebrate Assemblages in the Columbia River Basin.” Columbia River Inter-Tribal Fish Commission, December 2018. Accessed on June 21, 2020 by JM.

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