<P> Bright green blooms in freshwater systems are frequently a result of cyanobacteria (colloquially known as "blue - green algae" as a result of their confusing taxonomical history) such as Microcystis . Blooms may also consist of macroalgal (non-phytoplanktonic) species . These blooms are recognizable by large blades of algae that may wash up onto the shoreline . </P> <P> Of particular note are harmful algal blooms (HABs), which are algal bloom events involving toxic or otherwise harmful phytoplankton such as dinoflagellates of the genus Alexandrium and Karenia, or diatoms of the genus Pseudo-nitzschia . Such blooms often take on a red or brown hue and are known colloquially as red tides . </P> <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> <P> When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants . Algae tend to grow very quickly under high nutrient availability, but each alga is short - lived, and the result is a high concentration of dead organic matter which starts to decay . The decay process consumes dissolved oxygen in the water, resulting in hypoxic conditions . Without sufficient dissolved oxygen in the water, animals and plants may die off in large numbers . Use of an Olszewski tube can help combat these problems with hypolimnetic withdrawal . </P>

How do algal blooms affect other organisms in freshwater ecosystems