Ranging from microscopic, single-celled organisms to large seaweeds, algae are simple plants that form the base of food webs. Sometimes, however, their roles are more sinister. Under the right conditions, algae may grow out of control — and a few of these “blooms” produce toxins that can kill fish, mammals and birds, and may cause human illness or even death in extreme cases. Other algae are nontoxic, but eat up all of the oxygen in the water as they decay, clog the gills of fish and invertebrates, or smother corals and submerged aquatic vegetation. Still others discolor water, form huge, smelly piles on beaches or contaminate drinking water. Collectively, these events are called harmful algal blooms, or HABs.

Every U.S. coastal and Great Lakes state experiences HABs. These blooms are a national concern because they affect not only the health of people and marine ecosystems, but also the “health” of our economy — especially coastal communities dependent on the income of jobs generated through fishing and tourism. With climate change and increasing nutrient pollution potentially causing HABs to occur more often and in locations not previously affected, it's important for us to learn as much as we can about how and why they form and where they are, so that we can reduce their harmful effects.

NOAA is on the forefront of HAB research to better understand how and why these blooms form, and to improve detection and forecasting of these seasonal events. One of our top goals is to provide communities with advance warning so they can adequately plan for and deal with the adverse environmental, economic and health effects associated with HABs.