The answer is c.fish would die
Algae use the presence of increased nutrients and enhance their own growth. Tthey 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, such as fish, that depend on oxygen.