Algal bloom refers to the vigorous growth of algae or blue-green algae in the water, due to the enrichment of water body with mineral nutrients coming from fields, resulting in discoloration of the water body. This causes an increase in the biological oxygen demand (BOD), resulting in the death of fishes and other aquatic animals, due to suffocation.Red-tide is a phenomenon caused by algal blooms during which algae become so numerous that they discolour coastal waters (hence, the name "red tide").