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13 Texas Highway 18 bridge. It continues NNE for up to 1.7 kilometers to end in two small stock tanks (= Cow Pond). The spring water in the lower segment is consistently 200C and thus not likely to be reemerged upper segment water but rather another outflow from the same aquifer that initiates the flow of the upper section. The downstream extent of each segment varies depending upon prior climatic conditions. In March 1977 the lower segment was dry less than one kilometer NE of the Texas Highway 18 bridge but in August 1978 the two segments were con- nected by a substantial flow and the lower segment reached the Cow Pond. Similarly, the lower end of the upper segment may terminate nearly 200 meters SW of the location shown in Fig. 2. This variation is not especially seasonal but rather depends upon local climatic conditions- cool but dry winters and warm but occasionally wet summers. The water typically is highly saline with electrical conductivity between 13,000 and 17,000 micromhos/cm (Kennedy, 1977). MgS04 composes a substantial part of the dissolved solids. The saline nature of the water is re- flected in the absence of trees throughout the water courses and during all of our visits we avoided drinking the water. Kennedy (1977) reported the fish fauna in the upper segment to consist of Fundulus zebrinus, Lucania arva, Cyprinodon bovinus, Gambusia eiseri, G. affinis, G. nobilis, hybrids between the last two species, Lepomis cyanellus, and Cyprinus car io (in Diamond-Y Spring only). The lower segment lacks Gambusia eiseri and Cyprinus carpio. We have also obtained Notropis Zutrensis (especially after suspected releases of Cyprinodon) and Micropterus salmoides. We also have hearsay reports of catfish (= Ictalurus punctatus). In addition, Astyanax mexicanus was collected from Leon Springs in 1938. The absence of Gambusia eiseri in the lower segment is considered to re- flect inability to survive. None have been obtained subsequent to many being released on 28 February 1976. The Lepomis cyanellus were temporar- ily eliminated from the lower segment on 13 February 1976 and not found there again until August 1978 when the two segments were connected. On this date young Micropterus were also collected from the deep pools near Monsanto Well. Conditions in Leon Creek were relatively stable between 1965 and 1974 when Stephen E. Kennedy obtained a sample in January from Leon Creek adjacent to the Texas Highway 18 bridge. That August, Royal D. Suttkus collected Cyprinodon variegatus from the same location. The release of C. variegatus into Leon Creek is likely to be associated with the live bait industry. As live bait is commonly transported long distances, occasional populations of coastal sheepshead minnows are found far inland (Stevenson and Buchanan, 1973; Hubbs, et al., 1979). This specific release may have resulted from the transport of live bait from the Gulf Coast to the Pacific Coast: and the need to change water on this trip. There is little alternative available water on public land in trans-Pecos, Texas, and the saltine nature of Leon Creek would not harm estuarine bait fish. By November 1975 an extensive hybrid swarm was apparent in the collections by Anthony A. and Alice F. Echelle. The produc- tion of the swarm may well have been enhanced by the preference by C. bovinus females for C. nevadensis and C. macularius males over C. bovinus males (Paul V. Loiselle, pers. comm.). Turner and Liu (1977) report that most Cyprinodon interspecific hybrids are fertile so it is not surprising that the hybrid swarm flourished. The Echelles' observations resulted