![]() ![]() Many of the introduced fishes evolved in quieter waters, and couldīe considered “preadapted” for life in reservoirs above dams. At times, closed dams can shut off all downstream flow. Waters from the bottom tend to be cold and temperatures are fairly constant. Water for power generation is often drawn from the bottom of the reservoir. Instead, flow is regulated by electric power demands. Since dams create physical barriers to aquatic wildlife and severely alter the characteristics of the river’s flow, natural seasonal changes in flow and water temperature are virtually eliminated. ![]() Combined, the capacity of agricultural and municipal diversions actually exceeds the average annual flow of the river through Lee’s Ferry (in northern Arizona). It is of major commercial importance, providing electric power, water for irrigated crops and for 20 million people, of which only around 2.5 million actually live in the river basin.īy the time the river reaches the gulf, the water has been claimed by farmers, power companies, Indian nations, and both the U.S. The river has a fascinating history of human use over the last 10,000 years that includes fishing, farming, mining, and even steamboat transport! Today Square miles (625,000 km2) before it reaches (on a good day) the Gulf of California, some 10,000 feet (3000 m) lower in elevation. Originating high in the Rocky Mountains, the Colorado River drains seven North American states. The status of fishes in Mexico is less certain because there hasn’t been as much study of them. These factors have led to fragmentation and reduction of habitat available to native species. A myriad of factors has resulted in their precarious position, including exotic competitors (and predators), irrigation diversion, dams, and overuse of available water by our burgeoning human population. Of Arizona’s native species, at least two-thirds are listed as Threatened or Endangered by state or United States federal agencies. Unfortunately, most of the natives are disappearing with some of them virtually gone. The presence of these bodies of water resulted in an incredible array of animals in the region, everything from two inch (5 cm) long topminnows to six foot (1.8 m) long squawfish.Įven today Arizona boasts an impressive 30 or so native species of fish and at least twice as many introduced species. Though there isn’t much free-standing water today, as recently as 100 years ago several of the dry washes were true rivers. Traveling around the Sonoran Desert today, especially the northern portion, one would never suspect that it is home to more than 100 species of freshwater fishes. ![]()
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