Harmful Algal Blooms

Harmful algal blooms (HABs) impact our freshwater ponds, rivers, streams, lakes, and even reservoirs. These dangerous blooms occur when cyanobacteria accumulate and produce toxins that can threaten public and environmental health. Their impacts can be severe: a fish die-off at a favorite fishing spot, a pet poisoned after drinking from a contaminated lake, children with blisters and rashes from swimming in an affected river.

Understanding why algal blooms occur and the risks they present to our families and communities is an important part of reducing and preventing their impacts.

All 50 states have experienced a freshwater HAB within the past 15 years, yet there is no national database that tracks blooms or educates the public about the increase in HAB events.

To help fill this void, NRDC asked all 50 states for their HAB data and built an interactive map that pinpoints freshwater bodies that experienced HABs between 2008 and 2020. The map also shows how well each state monitored this growing problem and alerted the public to its impacts.

Click through the map to track HABs and learn if your state is doing enough to keep the public safe and educated. Urge your governor and state legislature to adopt, support, and fund proactive approaches to monitoring and responding to these toxic threats. 

Find Out How We Did Our Analysis >>

What Causes Harmful Algal Blooms, and What Can Be Done About Them?
 

Nutrient pollution is the primary driver of HABs across the country. Sources of this pollution range from fertilizers on farmland to pet waste on city streets. Nutrients like nitrogen and phosphorus are swept up by rainwater and make their way into our freshwater ecosystems, where they stoke cyanobacteria growth. Worse yet, rising carbon dioxide levels and temperatures, coupled with periods of intense precipitation brought on by climate change, increase the likelihood of nutrient pollution—and create perfect conditions for cyanobacteria to thrive.

NRDC advocates for policies that reduce nutrient pollution and protect the quality of our nation’s freshwater ecosystems.

• NRDC promotes agricultural policies that reward farmers for embracing soil health practices like cover cropping, diversifying crop rotations, and minimizing tillage. These measures reduce the need for synthetic fertilizers and other inputs that end up running off farmland and polluting waterways.
• NRDC works in cities to encourage widespread adoption of green infrastructure, including rain gardens, green roofs, and trees—all assets that capture rainwater where it falls. Every year, an estimated 10 trillion gallons of untreated stormwater washes off paved surfaces, travels through storm sewer systems, and flows into waterways. If not adequately controlled, the high levels of nutrients in this runoff can fuel HABs.
• NRDC fights to defend the Clean Water Act—a federal law that protects water quality in the United States—from attacks by the Trump administration and industry. One such attack includes the administration’s plan to repeal the Clean Water Rule and exclude more than half of the nation’s wetlands from federal protection. Wetlands perform important ecological functions, like filtering the kinds of nutrients that cause HABs.
• NRDC collaborates with government agencies, communities, and businesses to reduce excessive diversions from rivers, streams, and lakes. In many parts of the country, diverting water for cities, agriculture, and other uses changes the natural character of waterways and creates the warm, stagnant water conditions that are ripe for HABs.

Call on the Biden administration to take bold action for our environment

Take Action