A neutrally buoyant synthetic aquatic structure may be used to treat a body of water by removing nutrients and other materials from the water. According to another aspect of the invention, the synthetic structure may be used to promote and/or control the growth of aquatic species in a body of water. In a preferred embodiment of the invention, a denser-than-water ballast portion is suspended from buoyant material to stabilize and orient the synthetic structure. A high surface area structure for promoting biological growth may be provided. The ballast portion does not sink to the bottom of the body of water. Consequently, the high surface area structure may be maintained in the photic zone.