Why are algae blooms in ponds bad?
Algae grows in ponds when nutrient laden runoff washes into it. Nutrients (nitrogen and phosphorous) come from fertilizers, wastewater, etc. Sunlight and nutrients cause algae to grow. During the day, algae produce oxygen. But at night, algae respire and use the oxygen in the water. As a result, there is no oxygen left for the fish and they die before the algae start to produce oxygen again during the daylight. Eventually, the water may go septic.
