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What are red tides?

VIDEO: Learn about "red tides" and human health in this video from the U.S. Integrated Ocean Observing System®.

Red tide infographic

While harmful algal blooms (HABs) may occur anywhere along the nation's coast, especially during the summer, red tide events caused by blooms of the algae Karenia brevis are particularly common in coastal regions of Florida and Texas (Credit: NOAA). View and print this infographic and see the description below.

Harmful algal blooms can occur in coastal, Great Lakes, and fresh waters. While many people call these events "red tides" due to their red coloring, scientists prefer the term harmful algal blooms or HABs. Along Florida and Texas coasts, these blooms are primarily caused by the algae species Karenia brevis. Other algae species can form red tides, including colder water algae in the genus Alexandrium. Red tide can irritate people’s eyes and lungs. This can be more severe for those with preexisting respiratory conditions (such as asthma). The blooms can also cause large fish kills and discolored water along the coast.

A red tide bloom off the coast of Texas (Credit: NOAA).

A red tide bloom off the coast of Texas (Credit: NOAA).

Infographic Description

Red tide in Florida and Texas is caused by the rapid growth of a microscopic algae called Karenia brevis. When large amounts of this algae are present, it can cause a harmful algal bloom (HAB) that can be seen from space. NOAA issues HAB forecasts based on satellite imagery and cell counts of Karenia brevis collected in the field and analyzed by NOAA partners.

Why should you care?
Red tide in Florida and Texas produces a toxin that may have harmful effects on marine life. For people, The toxin may also become airborne, which can lead to eye irritation and respiratory issues. People with serious respiratory conditions such as asthma may experience more severe symptoms.

Making Choices
State and local resources are available to help beachgoers find nearby beaches and coastal areas that are not affected by red tide.