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Abstract Floodplain wetlands in the Colorado River system may serve as essential rearing and feeding areas for some native species, including the endangered razorback sucker and Colorado squawfish. Because channel and floodplain complexity have been reduced over the past 100 years by dam construction, flood control and riparian vegetational changes, the Recovery Implementation Program intends on restoring some floodplain function via levee removal. A concern with levee removal is the response of nonnative fishes. Many of the nonnative fishes in the Colorado River system are known to inhabit littoral or lentic habitats, consequently, levee removal may benefit nonnnative fishes more than native fishes. The overall strategy for the levee removal program is to remove levees (starting in the Green River system) from selected wetlands on a sequential temporal and spatial scale so the response of native and nonnative fish populations can be carefully evaluated. The design is based on selecting sites over a large spatial scale with the following criteria: 1) Geographic location (above and below Desolation/Gray Canyons, Block 1 and 2), 2) High versus low nonnative densities, 3) Depression versus terrace floodplain wetlands, and 4) Natural (sites that naturally inundate during high water years) versus application sites (sites where levees will be removed or breached). These criteria were used to develop a block design selection process for analysis purposes. Levees will not be removed in 1996, however, the methods for future levee removal activities, including sampling gear and sampling protocols, will be determined by the 1996 activities. In 1996, 12 naturally inundated sites should be monitored (6 in Block 1 and 6 in Block 2) for baseline data. The 1997 levee removal block design consists of selection of 10 application sites and 10 natural sites, above versus below Desolation/Gray Canyons. Two treatments will occur within each block. These are nonnative density and floodplain wetland type. Each treatment has two levels: high versus low nonnative densities and depression versus terrace habitats. Naturally flooded areas will be used to contrast responses in levee removal sites. Besides measuring the response of the fish community, macroinvertebrates, physical parameters and vegetation responses willbe documented in order to obtain a complete understanding of Colorado River wetland ecology. Macroinvertebrate production will be higher in floodplain wetlands than in the river channel, consequently, growth and possibly survivorship of fishes in floodplain wetlands may increase. The riparian vegetation and macrophyte community may change following levee removal. This shift could affect predator/prey interactions and food production. All of these questions need to be answered to determine what benefits levee removal will have for the endangered fishes. Following the initial year of levee removal evaluation, at least two additional years (1998-1999) of evaluation should follow.