ABSTRACT The ovoviviparous Kihansi spray toad Nectophrynoides asperginis is known from only one locality in the Udzungwa Mountains, Tanzania. At the time of discovery in 1996 the species occurred in a spray wetland habitat of about 4 ha maintained by spray from falls on the Kihansi River. River flow was diverted for hydropower production in late 1999, causing the habitat to desiccate, threatening the toad population and other plants and animals dependent on the spray wetland habitat. We conducted field studies from January 2001 to November 2002 in 12 visits, with additional counts through to June 2003. Here we report on the changes in population numbers in the light of the mitigation measures introduced from 2001 in an attempt to maintain a habitat suitable for the Kihansi spray toad. Some data on life history are presented. This small toad is now restricted to an area of less than 2 ha. Due to a reported population crash in late 2003, variously attributed to pesticide use upstream, chytrid fungus, or safari ants (Dorylus sp.), the Kihansi spray toad may be effectively extinct in the wild. The actual cause of the population crash is not known.