At the same time, even blooms that don't produce toxins can result in fish kills. When more algae is produced than can be consumed by predators, the excess will ultimately die and sink to the bottom and decompose in a process that can deplete the water of oxygen, sometimes killing fish, shellfish or other species in the area. They can produce other harmful effects too, such as blocking sunlight to underwater grasses that provide important habitat for crabs, clams, waterfowl, juvenile fish and other species. Without enough sunlight, the grass will die. Those sorts of things could occur.
Algae blooms are nothing new.
One of the Biblical plagues, in which the water is turned to blood, is thought to be a reference to red tides. Florida Indians told Spanish explorers of massive fish kills when the water turned red. There may be more algae blooms reported simply because more scientists are looking for them, and their impacts. On the other hand, red tides off Florida's West Coast seem to be lasting longer, and harmful algae that has contaminated shellfish in Maine for years has spread south into Massachusetts water. The Texas event is now 7 years old.