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( c> o C'.-'J (j) ~ ~ ( '- Animas River has been the major source of spring runoff flows in the lower San Juan River system. Tributaries downstream of the Animas contribute little to the total volume of the San Juan River. Ichthyofaunal surveys prior to extensive European settlement of the basin were very limited. However, early and subsequent surveys which are reviewed by Platania (1990) were sufficient to document a native fish fauna of nine species in the San Juan River. Eight species, Cutthroat trout (Oncorhvnchus clarki), roundtail chub (Gila robusta), Colorado squawfish (Ptvchocheilus lucius), speckled dace (Rhinichthvs osculus), flannelmouth sucker (Catostomus latioinnis), bluehead sucker (Catostomus discobolus), razorback sucker (Xvrauchen texanus), and mottled sculpin (Cottus bairdi) were all known by 1960. An additional species, bony tail chub (Gila eleqan) had been suggested as a possible member of the native icthyofauna, but its occurrence was not confirmed until 1991. Steven P. Platania (pers. corom.) examined museum specimens and found two individuals collected prior to 1941 thought to be ~. robusta, were~. eleqans. The limited nature of the surveys undertaken does not permit quantitative or even qualitative estimates of the abundance of any species. However, the size range of specimens, distribution of species collections and accounts by local residents strongly support the contention that each species had reproducing and viable populations in the San Juan River drainage. The San Juan River was largely ignored as a native and endangered fish resource in the years between 1960 and 1987. This was due to factors such as the fish poisoning project below the newly constructed Navajo Reservoir which was assumed to have eliminated or reduced endangered fish populations, relatively dense human settlement along the river near Farmington, in New Mexico, relatively large water depletions, and the degraded water quality in accessible areas associated with human activities. In addition, the remoteness of many parts of the river discouraged intensive or thorough studies of the river. The most significant native fish surveys of the San Juan River during this period include Olsen's pre impoundment study of Navajo Reservoir (Olsen 1962), Sublette (1977) and VTN Consolidated Inc., and Museum of Northern Arizona (1978) . Despite the limited nature of these collections, the persistence of the native fish fauna in recent years was documented by the collection of all species found prior to 1960 with the exception of bony tail chub. The first comprehensive study of fisheries in the San Juan River was initiated in 1987 when a three year study was implemented to obtain a more accurate characterization of the native fish fauna. The study, although encouraged in the 1979 biological opinion associated with the proposed Animas-La Plata project, was prompted by a proposal to re-establish the razorback sucker in the San Juan River. The study confirmed that Colorado'squawfish persist and reproduce in the San Juan River, and that the razorback sucker also 2