<P> Freshwater algal blooms are the result of an excess of nutrients , particularly some phosphates . The excess of nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes . They may also originate from household cleaning products containing phosphorus . These nutrients can then enter watersheds through water runoff . Excess carbon and nitrogen have also been suspected as causes . Presence of residual sodium carbonate acts as catalyst for the algae to bloom by providing dissolved carbon dioxide for enhanced photosynthesis in the presence of nutrients . </P>
what is most likely cause of algal blooms
an excess of nutrients , particularly some phosphates