In early July 2003, the spray irrigation maintenance team reported that they were no longer seeing any Kihansi Spray Toads in the Upper Spray Wetland. The decline began 2 weeks after an experimental intermittent bypass flow releases of 12 m3/s and 16 m3/s of water from the hydroelectric dam. A follow-up 1-hour nocturnal survey conducted in early August 2003 detected only 29 toads. This was shocking given that the population of the Kihansi Spray Toad in the Upper Spray Wetland in early June 2003 was approximately 18,000. A continuing and steady decline in the numbers of Kihansi Spray Toad was observed between June 2003 and May 2004 with the last recorded sightings of the Kihansi Spray Toad in May 2006. In 2009, IUCN formally listed the Kihansi Spray Toad as extinct-in-the-wild. Four prominent hypotheses have been proposed for the sudden decline and extinction in the wild of the Kihansi Spray Toad: (1) chytrid fungus Batrachochytrium dendrobatidis; (2) habitat alteration; (3) toxic contaminant; and (4) an interaction between Bd and a toxic contaminant. The best supported hypothesis is chytrid fungus. A retrospective analysis of 99 Kihansi Spray collected between 1986 and 2002 all tested negative for Bd; however five of eight specimens collected between August and November 2003 tested positive for Bd. Chytridiomycosis was also detected between 2004 and 2006 in two other anuran species occurring in spray wetlands in the Kihansi Gorge. The population recovery of the Kihansi Spray Toad in the Upper Spray Wetland following the installation of the spray irrigation system, and the undisturbed habitat in the Mhalala Spray Wetland where the Kihansi Spray Toad population also collapsed, provides countervailing evidence to the habitat alternation hypothesis. Experimental results on the toxicity of observed concentrations of endosulfan that were detected in reservoir sediments to the Kihansi Spray Toad were negative. A possible interaction between Bd and a toxic contaminant has not been evaluated.