A composition for mitigating, inhibiting, ameliorating and/or eliminating phytoplankton growth in a waterbody, the composition comprising an active ingredient at concentration of 80.0-99.5% (w/w) of the composition and a coating material at concentration of 0.5-20% (w/w) of the composition; wherein the critical surface tension of the composition is between 15-60 dyn/cm and wherein the relative density of the composition, prior to being submerged in water, is above 1 g/cm3.