(a) Cause: Algal blooms are caused by the increased nutrient availability in the water bodies. This high availability of phosphorus and nitrogen is in turn caused by the chemicals present in fertilizers that get dissolved in the soil and eventually get washed away to the water bodies. 

Affect: These algal blooms may shade out plants that would normally live lower in the water column resulting in a loss of biodiversity. Eutrophication can also result in the development of hypoxic conditions. This oxygen deficiency may cause the death of aquatic animals. They ultimately degrade the quality of water.

(b) Farmers in areas that are affected by algal blooms need to find alternative ways to fertilize the soil like using manures and techniques such as vermicomposting. Also, people must use cleaning agents and detergents that are biodegradable and that do that contain phosphates. To further reduce the amount of nutrients that are causing an overgrowth of algae in lakes and streams, laws need to be created that regulate the dumping of wastewater