(a) Algal bloom is the excess growth of planktonic algae that causes characteristic colouration of water. It may have caused due to passage of sewage and run off from the fields into the ponds. Nutrients present in sewage and run off cause nutrient enrichment or eutrophication particularly with nitrogen and phosphorus. Algal blooms cut off light for submerged plants. Water quality is greatly affected as there is decreased oxygen replenishment inside water. Decreased oxygen level is quiet harmful for aquatic life of the pond.