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Tusher Rapid is a naturally shallow riffle area which has been <br />modified somewhat by a ]ow weir (at river km 205.4) built in 1906 to <br />divert flow of the Green River for agricultural purposes, (Figure 8). <br />Of the water passing through the canal currently, 600 cfs are diverted <br />by the low dam into the canal. 505 cfs passes through a turbine which <br />drives a pump and 60 cfs is withdrawn for agricultural irrigation. The <br />balance of the flow of the Green River passes over the existing div- <br />ersion dam, and is joined by discharge from the powerhouse. The existing <br />structure is not believed to be an absolute barrier to migration of <br />adult Colorado squawfish, since specimens equipped with radio transmitters <br />have been tracked by researchers, showing movement upstream and downstream <br />over this structure. Figure 9 is a photograph of the existing structure <br />taken in July, 1983 during the period when Colorado squawfish were <br />migrating upstream to spawn. <br />Two sites in the area of Tusher Rapid are presently being invest- <br />igated as potential Colorado squawfish spawning habitat. Three Fords <br />Rapid, about 64 km upstream from Tusher Rapid, was confirmed as a <br />Colorado squawfish spawning site in 1983 and 1984. The other area is <br />the Tusher Rapid area proper, which is a suspected spawning site but, <br />has not been confirmed by fishery researchers to date. <br />The Tusher Rapid area is located between the aforementioned Three <br />Fords Rapid spawning area and the associated nursery area as shown in <br />Figure 4. The reach ,between the spawning site and the nursery area is <br />important because the non-mobile larvae are transported through this <br />area by river current. In this ]ife stage the organism is extremely <br />fragile and vulnerable and may be subject to mechanics] damage by <br />unnatural turbulance. <br />