In May 2016, Culex sitiens numbers sharply increased in a routine adult mosquito CO2 baited encephalitis virus surveillance trap in the northern Darwin suburb of Coconut Grove. A mosquito complaint was received from a resident in Nightcliff in July, with Cx. sitiens numbers also high in a mosquito trap subsequently set at the residence. To find the source of the high mosquito numbers, the Medical Entomology unit of the Department of Health (DoH) carried out larval mosquito surveys in May and found several blocked stormwater outfall drains, some of which were found to be breeding mosquitoes. The drains were treated for mosquito breeding, followed by maintenance works carried out by the City of Darwin (CoD) as part of the combined DoH and CoD mosquito engineering program. Subsequent mosquito surveillance results showed a dramatic decrease in mosquito numbers, highlighting the importance of the collaborative mosquito engineering program carried out in Darwin urban and the routine ground mosquito control program.