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River was intended to coincide with the period before and during spawning of razorback sucker. Removal efforts were intended to reduce the abundance of nonnative cyprinids before native larvae began drifting into nursery area habitats. Five sampling trips were conducted each year on the Green River. Sampling was conducted in 1998 from 11 May to 17 June, in 1999 from 26 April to 11 May and 31 May to 8 June, and in 2000 from ! 24 April to 24 May. This timing likely overlapped with native sucker spawning and drift, and preceded Colorado pikeminnow spawning (Bestgen et al. 1998). Sampling in 1998 and 1999 was suspended to wait for -high spring runoff conditions. In reference to flow recommendations (Muth et al. 2000), peak ~ discharge as measured at the USGS Green River at Green River gage (#090315000) in 1998 (24,100 cfs) was slightly above average, moderately wet in 1999 (30,000 cfs), and moderately dry (18,400 cfs) in 2000. The date of peak flow was 25 May in 1998, 23 June in 1999, and 3 June in 2000. The late peak in ~ 1999 was a result of emergency bypass releases at Flaming Gorge Dam due to heavy late spring precipitation. Sampling in 1999 was suspended for two weeks after the first three trips so that sampling would occur nearer to the anticipated peak flow (Figure 2a). On the Green River, where habitats usually , persisted throughout the sampling period each year, specific control sites above and below the study area were established during the first week of each year and were sampled on each trip. There were changes in sampling methods among the three years of study. In 1998, sampling , was conducted using an intensive block and seine technique with a three pass depletion to attempt complete removal of fish from the habitat (Trammell and Chart 1999b). However, only the portions of these habitats less than 1.2 m deep could be seined effectively. Some large washes were in excess of 500 m long, and only'/2 to 1/3 of the length was less than 1.2 m in depth. Beginning where habitat depth was 1.2 m or less, a series of cells was established by stretching nets across the backwater. Each cell created was approximately five meters wide and was seined with three passes to remove fish. This methodology was very time consuming and the full 50-mile reach could not be treated in one seven-day ~ sampling trip. Thus, focus of removal efforts narrowed through the five week season in 1998 to a series of habitats within a seven mile reach below the confluence with the San Rafael River in which razorback sucker larvae were comparatively abundant (Muth et al. 1998, Chart et al. 1999). The repeated seining ~ -5- 1