Algal blooms, and the rapid proliferation of photosynthetic plankton can ultimately end up depleting all the oxygen from a body of water

True  

Explanation:

The proliferation of phytoplankton (microalgae) may decrease the visibility which causes oxygen (O2) depletion because they consume important amounts of O2 during the night and cloudy days. An algal bloom refers to the sudden increase in the population of algae in water bodies. These algae consume O2 and block the sunlight from underwater plants. As the algae die and decompose, O2 concentration in the water decreases, and, in consequence, most aquatic life that depends on oxygen dies.