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Water development of the Logan River first began in 1860 when the first irrigation canal was built (Haws 1965). Today several large canals divert a large part of the Logan River flow. For example, the first diversion from the Logan River (Logan, Hyde Park and Smithfield Canal) above the State Dam diverted an average of 56.3 percent of the daily flow during the summer months and about the same percentage of the total annual runoff (U.S. Geological Survey 1976). The historical development of the Logan River, changes in water use, and legal controversies over water rights are documented in detail by Haws (1965). The diversion of water from streams as they enter the floodplain reduces streamflows and is especially critical to aquatic life during the low flows of summer. Therefore, the effect of stream channel alterations on aquatic organisms must also include the effect of reduced streamflows as part of the man-influenced river systems for all larger rivers in the Intermountain West. The ~aximum daily streamflow of the Logan River was recorded at 70.2 m3/sec (2,480 ft /sec) on May 24, 1907 (Corps of Engineers 1973). Flood conditions have occurred fairly often in the Blacksmith Fork and Logan Rivers when rapid melting of the mountain snowpack occurred between April and June. Eight major floods have occurred since 1900 that damaged agricultural crops in the flood- plain--mostly below the confluence of the Blacksmith Fork with the Logan River (Corps of Engineers 1976). According to local landowners, channelization of the streambeds in both rivers began over 50 years ago when the ranchers shovelled the streambed gravel by hand and transported this gravel from the stream by horse-drawn wagons. Short reaches of the rivers have been altered ever since that time. Today short reaches of the rivers are altered periodically with, backhoes and bulldozers by individual ranchers because of flooding in agricultural areas. Five study sites were selected that would provide information on three types of stream channel alterations (dredged, recently bulldozed, and old bulldozed) and two control areas in the floodplains of these rivers (Figure l). Logan Total Bulldozed Site A flood control project conducted by the U.S. Army Corps of Engineers on the Logan River in 1971 was criticized by local residents and the Utah Division of Wildlife Resources and the project even brought national attention (Stroud 1972). This 1.69 km (1.05 mile) reach was deepened and widened by bulldozer into a cross-section that was shaped like a trapezoid (Utah Division of Wild- life Resources 1972). In addition, all understory vegetation was removed and large trees near the channel were either removed or cut back so that shade and cover were greatly reduced. A reach of this stream channel, altered by bulldozer in 1971, was selected as a study site (Figure 1). A view of this site in 1976 (5 years after the alteration) is provided in Figure 8. Most of this reach has remained relatively unchanged since 1971 except for the downstream end. In April 1975, about 100 m at the lower end of the altered area was rechanneled by bulldozer, but. the remainder of this reach has not been altered by man since 1971. Logan total bulldozed refers to this entire reach, while Logan stable bulldozed refers to the portion not altered since 1971. Blacksmith Fork River Control Site 9