ABSTRACT
Glen Canyon Dam on the Colorado River has induced many changes in the physical and biological processes in the river. For the past decade, managers have tried to restore some of the important biological processes in the canyon by instituting an adaptive management strategy of controlled periods of high release from Glen Canyon Dam. These “controlled floods” are a large perturbation to the river system and have radical effects on the all of the organisms associated with it. This paper discusses the effect of the controlled floods on the aquatic food base, which includes algae, plants, zooplankton and macroinvertebrates. The Grand Canyon is also home to one of two remaining populations of the endangered Kanab Ambersnail. The controlled flooding has potentially detrimental consequences for their continued persistence as their habitat is within the high water zone. Additionally, the invasive New Zealand Mud Snail has recently colonized the tail waters of Glen Canyon Dam. This snail’s presence is altering the entire food web in the Grand Canyon and could further imperil the status of the native fish in the river, most of which are threatened or endangered.