The distribution, movements, activity range, and habitat use of the Concho water snake, Nerodia harteri paucirnaculata, were studied by mark-recapture and radio telemetry in a large lake system, in central Texas, USA. Concho water snake emigration and distribution were largely driven by alteration of habitat availability caused by fluctuating water levels. Habitat characteristics associated with the presence of snakes at the study area were turbid water, minimal wave action, a gentle shoreline gradient, a silt substrate, and a rocky shoreline. Males and gravid females were equally vagile, and the likelihood of a snake undertaking an emigrational movement was independent of age andlor reproductive condition. However, males had significantly more movement days than gravid females. Radio-tagged males had detectable move- ments on 64% of monitored days, compared to 43% of monitored days for gravid females. Mean activity range length was 278 m for males, 219 m for gravid females, and 210 m for juveniles. Concho water snakes generally selected retreat sites within 3 m of water, although gravid females selected sites as far as 15 m from water. As a management procedure for lake populations, we advocate increasing the vertical distri- bution of rocky shoreline. habitat, densities are greatly reduced (pers. Little is known about the spatial ecology of obs.), which may increase the likelihood of local snakes occurring in temporally volatile habitats. extirpations. With the impending construction Houston and Shine (1994) reported high dis- of Ivie Reservoir and the subsequent inundation persal rates for filesnakes (Acrochordus arafurae) of a significant portion of Concho water snake among billabongs, attributable to fluctuating habitat, assessment of the ecological attributes water levels. They also cite extensive wet season of lake populations became imperative. Of spe- movements for water pythons (Liasis fuscus) cial interest was a population persisting in E. V. (Madsen and Shne, unpubl. data). The above Spence Reservoir, constructed in 1969. Data ob- studies illustrate the importance of environmen- tained from the Spence Reservoir population tal variables on snake spatial ecology in natural may be applied to the future management of the systems. The present study deals with a popu- Ivie Reservoir population. lation of Concho water snakes in an artificial en-