Final: The Hoover Dam and Fish Populations

Last week I wrote about how the Bureau of Biological Survey’s chief Paul Redington championed the construction of the Hoover Dam as well as the 620,000 acre wildlife preserve that President Hoover created with an executive order. Redington boasted that the Boulder Canyon Wildlife Refuge would be an oasis in an otherwise arid region and that it would serve as a pit stop for migratory birds. In his report Redington writes, “It was a paradise throughout the year for Arizona quail, roadrunners, thrashers and other birds. In winter, swans, snow geese, many ducks, some shorebirds, waders, and a host of smaller migrant birds.” Redington’s report is heavily focused on the patterns of migratory birds and the benefits that the new lake and wildlife reserve would provide them but he mentions something interesting in passing. He says that the new lake will, “provide cover and food for the resident birds that are pushed back from the middle of the valley.” Obviously when he is talking about food he is talking about fish but the impact on local fish populations is never once explicitly stated in his report.

The creation of the Hoover Dam provides enough water and electricity to sustain Las Vegas, as well as the surrounding areas but it does so at a cost of local fish populations. The construction of the dam impacted the natural migratory routes of many different species of fish. One fish in particular, the Razorback Sucker, has had its population destroyed by the dam’s construction. According to the IUCN’s Red List of Threatened Species, “Spring migrations of adult Razorback Sucker were associated with spawning in historic accounts, and a variety of local and long-distance movements and habitat-use patterns have been documented.” But these migrations can no longer be completed and as a result the populations have suffered. The IUCN states that the population of Razorback Suckers is decreasing, despite environmental conservation efforts. In Lake Mohave, where the largest subpopulation of Razorback Suckers exists, the population was estimated to be between 44,000 and 60,000 in 1991 but in 2001 the population had significantly diminished to less than 3,000. One major reason for the sharp decline in these populations is habitat modification as a result of dam operations. Dam operations have greatly restricted the amount of suitable habitat; these detrimental changes include high winter flows, reduced high spring flows, altered river temperatures and reduced flooding.

A Razorback Sucker

Another example of a fish population being devastated by the construction of the Hoover Dam is the Bonytail fish. The Bonytail fish is the rarest of all the endangered fish in the Colorado River because conservation efforts did not start until years after people began to notice dwindling populations. As a result of this, scientists are still unsure of what the Bonytail’s preferred environment is. In his book, Restoring Colorado River Ecosystems: A Troubled Sense of Immensity, Robert Adler discusses the Bonytail populations and their decline. Adler writes, “the demise began shortly after 1900, as the river was progressively harnessed and regulated for water, power and flood control. Bonytail began to decline noticeably in the lower river throughout the first half of the 20th century. They were gone from the lower river by 1950, and experienced major declines elsewhere along the river in the 1950s, after the construction of main stem dams.” He also wrote about how local fauna populations declined downstream to upstream, in the same direction in which dams were progressively built. This makes conservation efforts that much harder since fish populations cannot be sustained where they cannot get access to food. 

A Bonytail

A third fish who has been put at risk due to the construction of dams is the Humpback Chub. The Humpback Chub is native to the whitewater regions of the Colorado River, which is why it was not discovered until 1946. In regards to the Humpback Chub, Adler writes, “The dam itself, with its accompanying changes in flow, temperature, and habitat, posed dramatic effects to native fish populations.” Yet despite the dramatic effects of the dam on native fish populations, data from as early as 2002 shows that Humpback Chub populations are stabilizing if not recovering.

A Humpback Chub

A common trait amongst all three of these fish is that they require on instinctual migratory paths to reach spawning waters and lay their eggs. Since the construction of the Hoover Dam and many dams like it along the Colorado River, fish populations have plummeted. There are very few large fish populations left in the river since most of them have been fragmented by dams or relocated to different waters in hopes they would prosper there. With the exception of the Humpback Chub, these populations have been declining ever since the dam’s construction and will only continue to plummet unless essential habitats, including required stream flows and necessary water quality, are legally protected.



  • Boulder Canyon Lake Wild Life Refuge Science, New Series, Vol. 77, No. 1994 (Mar. 17, 1933), pp. 276-277
  • Adler, Robert W., Restoring Colorado Ecosystems: A Troubled Sense of Immensity, Island Press, 2007.
  • Upper Colorado Endangered Fish Program. Accessed April 13, 2014. <>
  • Xyrauchen texanus (Razorback Sucker). Accessed April 13, 2014. <>

4 thoughts on “Final: The Hoover Dam and Fish Populations”

  1. I really liked this post; many people associate Herbert Hoover’s greatest accomplishment during his time as President as the start of building the Hoover Dam, so it’s interesting considering all of the environmental problems that resulted from his good intentions and how it puts a dent in his already tarnished record as President.

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