When large numbers of algae die off, what is a potential effect on fish populations?

When large numbers of algae die off, a significant consequence is a dramatic decrease in oxygen levels in the water. This phenomenon occurs because the decomposition of dead algae consumes dissolved oxygen, which is essential for the survival of most aquatic organisms, including fish. As the bacteria break down the algae, they utilize available oxygen, leading to hypoxic conditions (low oxygen levels) or even anoxic conditions (no oxygen), which can result in fish kills. In essence, the massive die-off of algae disrupts the ecological balance, creating an oxygen deficit that can suffocate fish and other aquatic life. This scenario highlights the intricate relationships within aquatic ecosystems and how changes in one population can have cascading effects on others.