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Five diversion structures on the San Juan River were all in <br />the New Mexico portion of the study area (Figures 4 and 5). Each <br />was a potential barrier to upstream fish movement, particularly <br />during low flow periods. The diversion structures ranged from <br />relatively inefficient soil-and-boulder dikes to concrete weirs <br />over which the entire river flowed. <br />The most upstream (within the study area) obstruction was <br />located just above the confluence of San Juan and La Plata rivers <br />and diverted water into Fruitland Irrigation Ditch. It consisted <br />of a boulder-and-debris levee. <br />The next diversion was a concrete weir located just <br />downstream of Fruitland. The entire river passed over this <br />structure. At extremely high flows (10,064 cfs (285 m3Js]), a <br />portion of the river passed around the weir and may have allowed <br />upstream movement of fishes. <br />The pump station diversion (Four Corners Power Plant), was <br />located three miles (4.8 km) downstream of the concrete weir at <br />Fruitland. At most discharges, it was probably only a moderate <br />impediment to upstream movement of fishes. <br />The Hogback diversion, constructed of large boulders, was <br />located between Fruitland and Shiprock. During our study, this <br />diversion was passible by fish until September 1987 when it was <br />reconstructed and diverted all flow into the Hogback Canal. <br />The most downstream diversion, at Cudei, was the only one <br />below Shiprock and was traversed on all trips with little <br />difficulty. This structure diverted water into Cudei Canal. <br />11