Red tides, a common term for the more proper name of “harmful algal blooms” (HABs), occur when colonies of algae—simple ocean plants that live in the sea—grow out of control while producing toxic or harmful effects on people, fish, shellfish, marine mammals and birds. The human illnesses caused by HABs, though rare, can be debilitating or even fatal. As the name suggests, the bloom of algae often turns the water red.
But not all algal blooms are harmful. Most blooms, in fact, are beneficial because the tiny plants are food for animals in the ocean. In fact, they are the major source of energy that fuels the ocean food web.