Mosquito Dunks float on water and will keep on working for 30 days or longer under typical environmental conditions. While floating, they slowly release a long-term, biological mosquito larvicide at the water's surface. This larvicide (Bacillus thuringiensis israelensis) gradually settles in the water where it is eaten by mosquito larvae growing there. Mosquito Dunks may be used in all types of containerized standing water sites, except finished, treated drinking water, where mosquito larvae grow. Alternated wetting and drying will not reduce their effectiveness.

To prevent them from being washed away, the dunks can be anchored using a string tied through the center hole, or they can be stalked in place.