Abstract: A device for releasing mosquito larvae-killing material into a body of water includes a porous container having mosquito larvae-killing material therein. There are buoyancy means associated with the container to raise it above the bottom surface of a body of water and out of any silt that may be at the bottom. There is a weight adjacent one end of the container which cooperates with the buoyancy means to maintain the container in a generally upright position within the body of water. There is a flexible connection between that portion of the container holding the larvae-killing material and the weight to permit the container to move as water flows by it and to prevent the container from being buried in surrounding silt.