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Implementation Strategy The overall strategy for this program is to remove levees from selected floodplain wetlands on a sequential temporal and spatial scale so the response of native 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), 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. In addition to these criteria we based the strategy on the following assumptions: 1) Initial efforts would occur in the Green River system, 2) A period of three years would be required to evaluate each application activity, and 3) Adjustments to the strategy would occur as warranted based on new information. 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 sites should be monitored (6 in Block 1 and 6 in Block 2) for baseline data. Within each block, 4 sites will flood naturally and two sites will be controls. Specific activities for levee removal in 1997 are identified below. These activities are followed by two additional years (1998-1999) of evaluation. Additional levees for breaching or removal in out years (1998 and beyond) will be identified after the first full year of evaluation (1998) and analysis of information collected during the first two levee removal field seasons (1997 and 1998) is complete. Levee Removal Activities Green River The 1997 levee removal block design consists of selection of 10 application sites and 10 natural sites, above versus below Desolation/Gray Canyons (Table 1). 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 application sites. That is, for each treatment combination of the values observed in the natural sites will used as a simple contrast to application sites. We have identified approximately 30 potential candidate sites to fill in this strategic design plan for levee removal in 1997. These sites are listed in appropriate block (Blocks 2 and 3). The selection of final sites for levee removal or breaching from this list will be based on the following factors: 1) relative flood-ability and drain-ability, 2) landowner willingness to participate, and 3) contaminants.