Harmful Increasing Waterbody Algal Blooms Are Nationwide Threat

On July 12, 2017, the CDC published information about harmful algal blooms. Harmful algal blooms can produce toxins that are dangerous to people, animals, and the environment. Harmful algal blooms have occurred in every region of the United States. In 2014, 38 states responded to a survey about harmful algal blooms, and more than half reported that such blooms occur every year in a freshwater body. All coastal states have reported harmful algal blooms in marine waters, and these blooms also have been reported in all the Great Lakes. Evidence suggests that harmful algal blooms are increasing in number and severity because of changing temperatures, farming practices, storm water runoff, and wastewater overflows.


During warm weather, microscopic plant-like organisms—algae and cyanobacteria—are more likely to overgrow in rivers, lakes, and oceans. These overgrowths, called algal blooms, occur across the country. Sometimes they are just eyesores—an unpleasant scum or mats of green, red, blue, or brown organisms in the water that look or smell bad. Sometimes they also cause harm to people, animals, and the environment. In this case, they are known as harmful algal blooms. But observers cannot tell if a bloom is harmful just by looking at it. Not all blooms are easy to see—toxins can be present even when an observer cannot see the bloom.


Harmful algal blooms can produce toxins that can make people and animals sick. They also can block sunlight or use up a lot of oxygen in a body of water, which kills fish and plants in the water. Harmful algal bloom toxins have caused the shutdown of the water supply in a major U.S. city; killed wildlife and pets; and sickened hundreds of people with a variety of skin, breathing, neurological, and stomach symptoms.


People and animals can be exposed to algal toxins in many ways. Exposure can occur when swimming or coming in direct contact with the toxins, breathing in the toxins, swallowing contaminated water that contains toxins, or eating seafood contaminated with toxins. Animals can often be the first affected because they are more likely to swim or drink from bodies of water that contain algal blooms.


Because harmful algal blooms affect people, animals, and the environment, it is important to document when they happen, where they happen, and whether they cause illness. The CDC’s One Health Harmful Algal Bloom System (OHHABS) is a web-based national reporting system for harmful algal blooms. State and territorial public health departments and their designated environmental health or animal health partners can use this voluntary system to report harmful algal bloom events and associated illnesses in people and animals. The data collected helps the CDC and its partners learn more about these blooms and understand how to best prevent the illnesses they cause.


Harmful algal blooms are an example of a One Health issue. The One Health approach recognizes that human, animal, and environmental health are connected. Using this approach to track harmful blooms highlights the opportunity for human health, animal health, and environmental health experts to work together to effectively address the problems that harmful algal blooms can cause.


See the CDC Feature