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within each cell produced few additional fish. The usefulness of the lengthy but more complete depletion ~ effort was marginal compared to the untreated habitat area, suggesting modifications to the sampling protocol were necessary. In 1999 sampling intensity was reduced in individual backwaters by eliminating individual cells ~ and expanding removal efforts to cover the full 50-mile (80.5 km) reach. During the first three trips in 1999, at least two removal passes were made in each of these large flooded habitats. A series of seine hauls was made in each habitat until all seinable area was covered at least twice; however, during the R final two weeks, the seinable area was covered only once with a series of hauls due to time constraints. In 1999 exclusion block nets were installed in three selected flooded wash habitats (School Bus Wash, White Wash, and Red Wash). These habitats were selected because they were too large and deep to be M effectively seined, but could be easily blocked. Block nets were 6.4 mm plastic mesh suspended from 15.9 mm steel rebar and 6.4 mm shock cord by zipties. The block nets were 2 to 3 m high and $ to 15 m wide, depending on the width of the habitat. Nets were installed inside the mouth of the washes while they were dry. When the washes became inundated at higher discharge, the block nets allowed larvae and smaller fishes to pass through the netting but excluded larger fishes, creating an area that had potentially fewer predators and less competition for resources. In 2000, the Program recommended discontinuation of the block nets; thus, all habitats were sampled similarly as in 1999, but no habitats were blocked. 2.2.2 Colorado River Methods In the Colorado River, removal efforts were intended primarily to benefit Colorado pikeminnow and other native species. Colorado pikeminnow are known to spawn on the descending limb of the hydrograph in the Colorado River above Loma near RM 154 (Anderson 1999) and possibly just below the Colorado/Utah state line, or below Westwater Canyon (Trammell and Chart 1999d). Once hatched, larvae from these spawning sites drift downstream into the sampling reaches chosen for removal efforts. Removal efforts were conducted after the spring peak flows for four weeks in 1998 and 1999, and for five weeks in 2000. The sampling periods generally began well after the peak flow because no backwater -6-