Red tides are a type of harmful algal bloom, and they occur worldwide. There are over 300 species of red tide, and within the United States, these blooms appear in three main coastal areas, although researchers are studying bigger blooms in regions where they were once mitigated before. Red tides are caused by several different microorganisms, all phytoplankton that use light energy to grow.

In the U.S., red tides predate Spanish settlers; history shows Native Americans were aware of the algae’s existence. But with human influence and climate change, the nutrient-hungry algae is exacerbated, inflicting harm on animals and people alike—and ruining spring break plans.

At least three species of dinoflagellates and one diatom species are responsible for the toxic