Sometimes, green algae such as Chlorella, Scenedesmus and Spirogyra, etc., grow in excess in water bodies and impart green colour to the water. These are called algal blooms. Red dinoflagellates (Gonyaulax)’grow in abundance in sea and impart red colour to the ocean. This looks like red tides. Due to algal blooms and red tide, the animal life declines as these makes toxins and deficiency of oxygen inside water.