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<br />OD17~3 <br /> <br />TROUT POPULATION AND AQUATIC HABITAT <br /> <br />Outcome <br /> <br />The Test had little acute effect on the aquatic ecosystem of <br />the San Juan River for the six days the test was conducted. <br />Decreases in river stage, wetted perimeter, and average <br />habitat depth did not result in direct mortality of fish. <br />However, habitat of fish was clearly reduced, in all likelihood <br />forcing fish to use the deeper runs and pools for resting and <br />escape cover; this could result in crowding and possible stress <br />of fish over an extended period of time. Reductions in wetted <br />perimeter will decrease macro invertebrate production, but <br />food for fish is not expected to be limited even at lower flows. <br /> <br />Over a longer period, the habitat reduction and water quality <br />changes with summer flow reductions could have adverse <br />effects on the trout fishery. For example, if Citizens Ditch <br />diverted their 160 cfs water right, impacts would increase <br />below Citizens Ditch. During the Test, habitat was clearly <br />reduced in this area, and this could result in crowding and <br />possibly stress of fish over an extended period. Reduction in <br />depth of riffles could limit available secure feeding areas for <br />such drift feeders as trout and such bottom scrapers as native <br />suckers. <br /> <br />In general, prolonged low flows or frequent low flow periods <br />could reduce fish populations ~s a result of diminished <br />habitat area, reduced habitat depth, and higher water <br />temperatures. Chronic effects cannot be assessed at this ~ <br />time, but a monitoring program is recommended to <br />determine long-term impacts of low flows. <br /> <br />Summer Low Flow Test Report - November 2001 <br /> <br />-13- <br />