River environments are some of the most highly modified ecosystems in the world. Dams, channelization, and water diversions disrupt ecological interactions and connectivity (Ligon et al. 1995; Power et al. 1996; Ward et al. 1999). Altered flow regimes and consequent changes to downstream aquatic habitats can have negative impacts on endemic aquatic populations (Lind et al. 1996; Freeman et al. 2001; Marchetti and Moyle 2001). In western North America, a variety of amphibians use streams and rivers for oviposition and larval development, including the Western Toad (Anaxyrus boreus) and Arroyo Toad (A. californicus), California ( aricha rivularis), Rough-skinned (T. granulosa), and Sierra (T. sierrae) newts, and the Foothill Yellow-legged Frog (Rana boylii). These species have reproductive cycles that are adapted to the natural flow regime and thus can be particularly vulnerable to altered flows in managed rivers. Conservation of these species therefore depends in part on understanding the impacts of regulated flow regimes on instream physical habitat conditions and whether habitat remains suitable during critical reproductive and growing seasons.