This paper describes the temporal and spatial abundance of the mosquito fauna of the Ross River Dam (Stage 1) in northern Queensland, Australia. Culex annulirostris, Anopheles annulipes s.l., Mansonia uniformis, Mansonia septempunctata, and the nondam breeding Aedes vigilax were the major species collected by dry ice-supplemented light traps set at various distances from the edge of the reservoir. To estimate the level of arbovirus activity in these different zones, sentinel chicken flocks were bled 4 times a year and their antibody conversion rates determined by the hemagglutination-inhibition test. Although mosquito abundance at sites close to the reservoir were 1.5-6.1 times higher than at the more distant sites, arbovirus conversion rates, particularly to the alphaviruses Ross River and Sindbis, varied according to zone and year, suggesting that risk of infection was no greater around the dam than elsewhere.