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removal within treatment reaches only was conducted separately (ANCOVA) using data from five unique ~ backwaters (all flooded tributary mouths) sampled on most trips in each year in the Green River. Finally, we examined NNC CPE in each of four of these backwaters on consecutive removal seine hauls during each trip in 1998. All tests were considered significant if P < 0.05. ~ On the Colorado River, backwaters were ephemeral because decreasing flows during the sampling periods dried many habitats as others formed. Consequently few backwaters were sampled more than one time. Because CPE could not be directly compared for the same backwater between ~ removal trips, mean CPE was calculated from all treated habitats in a reach for each of the three river reaches. A mean CPE was calculated separately for each of the control areas between treatment areas. Mean CPE was then compared among years, reaches and between treatment and control reaches using ~ ANCOVA, and trips were specified as a covariate. Young-of-year Colorado pikeminnow and other native and nonnative fish are monitored each fall by seining backwaters in the Green and Colorado rivers as a component of the ISMP. The ISMP seine ' data were used to evaluate native and nonnative fish response to the removal efforts. Mean CPE for 1998 to 2000 was compared graphically to the long-term mean CPE (ISMP) and associated 95% confidence intervals. 3.0 RESULTS 3.1 Green River NNC Removal Effort varied from year to year due to discharge, amount of available habitat, sampling protocols, and number of river miles sampled. Effort in 1998 was 88,149 m2 seined over aseven-mile treatment reach, and 5,515 m~ in the control reach. Effort in 1999 and 2000 was distributed over 50 river miles. In ~ 1999, total area seined was 80,160 m2 in the treatment reach, and 17,167 m2 in the control reach. In 2000, area seined was 119,115 m2 in the treatment reach and 15,620 m2 in the control reach. Since sampling preceded spawning of Colorado pikeminnow, all captured pikeminnow were at ~ least age-1. In 1998, the Colorado pikeminnow were primarily 140-200 mm TL, and were likely of the -$- 1