Immature mosquitoes develop in standing water bodies such as ponds. While a fountain helps move the water and reduces the risk of mosquitoes breeding in your pond, several other techniques can control a mosquito infestation in your pond.
Mosquito eggs take some time to develop into adults. Changing the water in your pond and fountain twice a week prevents any mosquito eggs from fully developing, reducing the number of adult mosquitoes in the area.
Insecticides also effectively kill mosquitoes, but many of them can adversely affect other organisms in ponds and fountains. A natural bacterium, Bacillus thuringiensis israelensis (Bti), infects and kills only insect larvae. Bti comes in blocks that you can float in ponds and fountains.
Some fish feed on mosquito larvae and effectively kill the mosquitoes in ponds and fountains. These include goldfish and mosquito fish (Gambusia). Minimising slopes in your pond allows these fish to reach every part of the pond and helps them eat more mosquitoes.