Reservoirs on a Great Plains Stream Affect Downstream Habitat and Fish Assemblages

Abstract

ABSTRACT Reservoirs can markedly alter downstream reaches of streams and often reduce multiple, braided channels to a single channel in the Great Plains. The Laramie River downstream from Grayrocks Reservoir in southeastern Wyoming is undergoing such morphological changes. Along 10 transects measured in 1991, we saw 3–9 abandoned channels and a single channel with water. The mean incision among remaining channels with water was 1.7 m. We sampled fish assemblages from the main channel, remnant side channels, and backwaters. Species richness and diversity were greatest in backwaters and greater in the main channel than in side channels. Side-channel and main-channel fish assemblages differed substantially. Side channels contained fishes common in small streams, whereas the main channel contained fishes usually associated with larger streams.