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back sucker was listed, the SCLDF filed another lawsuit and compelled the FWS to designate its critical habitat. The FWS then decided to combine the designation for the razorback with designations for the other three list- ed fish species. The final designation of critical habitat for all four fishes was published in March 1994. Critical habitat is defined as a "geographic area" with the physical and biological features that are "essential" to the conservation of a listed species, whether currently occupied by that species or not. Under the ESA, con- serving a listed species means bringing it back to the point at which it no longer needs to be protected by the ESA - to the point of recovery and de-listing. The geographic area designated as critical habitat may there- fore be greater than what is needed for survival. The FWS may exclude areas from the designation if the eco- nomic impacts of the designation outweigh the benefits of designation, but only where such an exclusion will not undermine species survival. Where the economic impacts do not outweigh the benefits to the listed species, the designation must not only include areas to avoid extinction, but also those needed for recovery. In designating critical habitat for the listed fishes of the Colorado River, the FWS identified the following phys- ical and biological attributes or "constituent elements" as essential to recovery: ... Water in sufficient quantity and quality delivered to a specific location and in a hydrologic regime as need- ed for any life stage of the listed fishes. ... Physical habitat needed for spawning, nursery, feed- ing, and rearing, including the river corridors between such areas and bottomlands, side channels, secondary channels, oxbows, backwaters, and other such habitat within the 100 year floodplain. ... Biological environment including food and nutrient supply and freedom from competition with and preda- tion by non-native fishes. The FWS did not quantify these elements or specify their location but designated critical habitat as wherev- er such constituent elements occurred for each of the four listed fishes within 1,980 river and reservoir miles throughout the Colorado River Basin and the 100 year floodplain for those reaches. The designation was bounded by some river reaches that may not be presently occupied by the listed fishes, but fell well short of their historic range. For example, no critical habitat for the Colorado squawfish was designated in the Lower Basin. Several reaches were dropped from the designation in the Lower Basin for biological rea- sons: the Colorado River from Davis Dam downstream to Toprock Marsh for the bonytail, and several tribu- taries to the upper Salt, Verde, and Gila Rivers and the mainstem of the Verde River from Sullivan Lake to Perkinsville for the razorback. But no reaches were eliminated based on the economic or other impacts of the designation. The FWS concluded that most of the economic impacts were generated by the listing of the fishes and the consequent protections under the ESA other than critical habitat designation. The finally des- ignated river reaches are shown in Figures 2-5. The FWS was clear that the designation was not meant to include all land within the 100 year floodplain - it only covered those areas in which the identified con- stituent elements were present, which could exclude most developed areas of the floodplain, and much of the shoreline for the designated reaches was publicly owned. Nor does the designation imply that any reser- voirs along the specified river reaches have to be con- tinuously maintained at their full pool elevations - the reservoirs and their pool elevations in the Lower 45