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.{ • • ` -16- In order to gain acceptance by the public and by State and federal fish and wildlife agencies of their dredging and streambank modification proposals, the Bureau of Reclamation is required by law to provide adequate mitigation for lost fish and wildlife habitat and lost fishing and hunting opportunities. They attempt to accomplish this by constructing artificial backwater lakes, or by installing water intake structures to marshes cut off from the river by channelization, or by purchasing habitat for wildlife refuges. Because of the shortcomings inherent in trying to improve on nature, so to speak, or to "create" wildlife habitat, mitigation has never fully compensated for lost fishery values. For example, artificial backwater lakes take nearly a decade to mature (ecologically) to the point where they even begin to mitigate for original classes. Tending to offset somewhat the losses of natural river habitat has been a network of irrigation canals and drains which have created habitat for many of the same species that would normally occupy the natural backwaters and oxbow lakes. However, removal of aquatic macrophytes by "draglining", and occasional fish kills due to improper pesticide application, act to reduce fish production in these waters. With over 5,600 km of irrigation canals and drains in the Imperial and. Palo Verde valleys, the cost. of efforts to control aquatic macrophytes is substantial. In an effort to find a cheaper alternative, the plant-eating Mossambique mouthbrooder (TiZapui mossambica) has been introduced from Africa into irrigation canals in the Palo Verde and Imperial valleys. It has been only partially successful,. however, and aquatic weeds must still be controlled by dredging. Thus, in addition to problems caused by dredging, game fishes must now cope with pressures of predation and competition from an exotic species totally alien to North America. OUTLOOK FOR THE FUTURE The conditions outlined above are examples of some of the major problems involved in maintaining suitable aquatic habitat and recreational sport fishing in the lower Colorado River. Numerous lesser problems and conflicting uses exist that I have not discussed, such as domestic pollution, eutrophication, and pesticide contamination, but these have thus far been less of a problem than dredging, streambank alteration, and siltation.- Unfortunately, it is likely that all of these problems will increase in the future as the pressures for development in the American Southwest and the demands for Colorado River water become more intense. Presently the waters of the Colorado are apportioned between the upper basin states and lower basin states by a compact. Until recently, the demand for Colorado River water in the upper basin states has not been as great as in the lower basin states. Now, however, the upper basin states are beginning to appropriate more of their legal share of water, as is Mexico which has also been guaranteed water that meets minimum salinity standards. Add to this a demand for water to cool proposed nuclear power plants or existing