Algal Blooms, Dead Zones, and Acidification High quantities of nutrients in the water from industrial crop fertilizers and animal waste cause excessive aquatic plant growth — a process known as “eutrophication,” which, in turn, causes “hypoxia,” or water that is low in oxygen. Harmful algal blooms (or HABs) occur when aquatic algae grow rapidly out of control. Some types of HABs produce biotoxins, which can kill fish and other aquatic life and cause human illnesses, while ot