About this Article
Written by: Erik Thompson
Written on: September 1st, 2001
Tags: environmental engineering, energy & sustainability
Thumbnail by: U.S. Geological Survey/Wikimedia Commons
About the Author
In the spring of 2001, Erik Thompson was a senior majoring in Biomedical Engineering at the University of Southern California.
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Volume IV Issue I > Engineering a More Fish-Friendly Dam
Thousands of Americans have come to rely on dams not only as a source of inexpensive power, but also for irrigation and navigational needs. In spite of their benefits, dams have come under fire because of the role they have played in contributing to the decline of Pacific Northwest salmon populations. To avoid dam removal, engineers have worked to design more fish friendly dams that can continue to produce electricity but minimize the harm done to migrating salmon. This paper provides background on the current controversy over dams and discusses the effects of dams on migratory salmon and the steps engineers are taking to alleviate the problem.


The life cycle of a salmon is one of the most unique in all of nature. Young Pacific Northwest salmon face a long, arduous journey as they travel from spawning grounds high in mountain streams, through the Columbia River Basin, and out to the Pacific Ocean. After reaching the ocean, an adult salmon will spend anywhere from two to six years at sea before making the return trip inland to spawn in the same streambeds of their birth.

A Perilous Journey Home

Under the best of circumstances, the journey from a salmon's spawning grounds to the ocean and back again is a perilous one, and a migrating salmon faces many dangers during the trip. Predatory species such as Pike minnows hungry birds, and Kodiak bears (see Fig. 1) anxiously await any opportunity to feast on the salmon as they pass by. Environmental conditions, such as water temperature and flow rate, can also adversely affect the survival rate of young ocean bound salmon. Returning adults must fight their way upstream, battling the swift currents of rapids and waterfalls, to return to their native spawning grounds. In spite of these hardships, salmon once flourished in the Columbia River.
Greg Wilker/U.S. Fish & Wildlife Service
Figure 1: One of the salmon's predators, the Kodiak bear feasts on salmon attempting to swim upstream.
In the early 1880's, the advent of commercial fishing marked the first time records of salmon population were regularly kept. At the turn of the nineteenth century, the average number of adult salmon returning to spawn in the Columbia River numbered between 10 and 14 million. During the last century, that number drastically declined, with current returning salmon counts hovering between 1 and 2 million [1]. In 1995, of the nearly 1000 original species of salmon and steelhead, 106 were extinct and 314 were listed as endangered [2].
Many factors account for this drastic decline in the salmon population. Although natural factors such as climate variations do affect salmon populations, most of the decline in population has been attributed to human interference. Human factors are three-fold: 1) population decline as a result of fishing; 2) habitat destruction due to logging, construction, agriculture, and dams; and finally the most significant, 3) destruction and blockage of migratory routes by hydroelectric dams. Dams account for nearly 99% of migratory salmon deaths, and have been the subject of much controversy in recent years [3].

The Whole Dam Problem

Because of the extreme negative impact dams have had on salmon migratory routes, many environmentalists have called for the complete removal of some Pacific Northwest dams. While proponents of dam removal present the solution as an easy and obvious step towards the recovery of salmon, this seemingly simple solution comes with a huge price. Removing dams would indeed help to restore natural salmon habitat, but the destruction of dams would also carry enormous economic and even environmental consequences for the Pacific Northwest.