Colorado River | WWF

Colorado River

About the Area

The Colorado river, historically one of the most powerful rivers in the world, drops two miles in elevation from its headwaters to the Gulf of California that results in turbid, fast-flowing waters.
This in addition to the basin's geographic isolation, have led to an exceptional freshwater fauna with morphological adaptations to rapid water currents. Within this relatively species-poor ecoregion, 14 endemic fish species occur, that are struggling for survival today due to a severely altered environment that has rendered certain parts of the river almost dry.

Local Species
Imperiled endemic fish species include the largest North American minnow, the Colorado squawfish (Ptychocheilus lucius), and the oddly shaped Razorback sucker (Xyrauchen texanus). Other fish species found in the turbid fast-flowing waters include Flannelmouth sucker (Catostomus latipinnis), Sonora sucker (Catostomus insignis), and Desert sucker (Catostomus clarki).

Found in some of the smaller tributaries of the Colorado and in springs in this ecoregion are species of special concern due to their restricted ranges. These include Little Colorado spinedace (Lepidomeda vittata), Kendall warm springs dace (Rhinichthys osculus), Desert pupfish (Cyprinodon macularius), and Springfish (Crenichthys baileyi).

The Colorado squawfish, yet another endangered species, is the largest North American minnow, attaining a length of up to 59 inches and weighing between 20 to 35 kg. A number of fish are endemic to the Gila drainage, one of the larger tributaries to the Colorado. These include Gila trout (Oncorhynchus gilae), Gila topminnow (Poeciliopsis occidentalis), Roundtail chub (Gila robusta), and Spikedace (Meda fulgida).

Springs in this ecoregion also support several species of endemic snails, including Overton assiminea (Assiminea sp.), Grand Wash springsnail (Fontelicella sp.), Pahranagat pebblesnail (Fluminicola merriami), Moapa pebblesnail (Fluminicola avernalis), and Hot Creek pebblesnail (Fluminicola sp.). Riparian forests provide critical habitat for the endangered Willow flycatcher (Empidonax trailii).

This unusual ecosystem has been severely damaged by development, dams, irrigation projects and water withdrawals, pollution, altered thermal regimes, and introduced species. Today, only a tiny fraction of intact habitat remains and these remnants face continued threat from livestock grazing and other development pressures.


700,000 sq. km (270,000 sq. miles)

Habitat type:
Large Rivers

Geographic Location:
North America: Wyoming, Colorado, Utah, Arizona, New Mexico, Nevada, and California and Mexico at its northern border

Conservation Status:

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