Houses have been built around a small retention pond, increasing the fertilizer runoff into the pond. This has led to algal blooms in the pond which periodically reduce the amount of dissolved oxygen available in the water. What will be the most likely long term effect on the fish population living in the pond if the situation with the fertilizer does not change

Algae blooms are the consequence of large amounts of fertilizers in the water. Algae use the presence of increased nutrients and enhance their own growth. It is known that they produce an oxygen in the photosynthesis, so it is not a problem while they are still alive. But when these organisms die, their decomposition begins. For the process of decomposition, the oxygen is needed and ultimately it will be depleted from a body of water. This could lead to the death of aquatic animals that depend on oxygen. So, in the population will survive only those who are able deal with the lack of oxygen in the water