Harmful Algal Blooms (HABs) refer to toxic algae blooms, which can affect humans, pets and ecosystems.

Canoes sit out of the water near an algae bloom fed by nutrients

HABs occur when certain types of algae grow excessively in waterbodies, producing toxins or other harmful effects on ecosystems, human health and local economies. While algae are a natural component of aquatic environments, some species can multiply rapidly under the right conditions, leading to serious environmental and public health concerns. HABs can happen in both freshwater and marine environments and are an issue of concern regionally, nationally, and globally.

In freshwater ecosystems across New England and New York, HABs are primarily caused by cyanobacteria, or blue-green algae. Freshwater HABs frequently result in recreational advisories and beach closures due to health risks.

In marine environments, HABs are typically caused by microscopic algae, such as dinoflagellates and diatoms. These organisms can produce potent toxins that accumulate in shellfish, leading to shellfish bed closures and economic losses for coastal communities.

Causes of Harmful Algae Blooms

HABs develop due to a combination of environmental factors. High levels of nitrogen and phosphorus, often from sources such as agricultural runoff, stormwater and wastewater effluent, contribute to the formation of blooms by providing nutrients for algae to grow. Rising water temperatures also create ideal conditions for algae to thrive. Calm water conditions, such as those caused by drought or low water circulation, allow algal species to persist and spread. During the summer, increased sunlight and longer days provide algae with the energy they need to survive and grow.

Impacts of Harmful Algae Blooms

HABs have a range of harmful effects on humans, animals, aquatic ecosystems, and local economies. For humans, toxins produced by cyanobacteria and marine algae can cause skin rashes, gastrointestinal illness, respiratory issues, and, in severe cases, liver damage. Consuming contaminated shellfish can result in serious illnesses, such as paralytic shellfish poisoning. Animals, especially those that rely on aquatic environments, are also vulnerable to the effects of HABs. Toxins can be harmful or even fatal to pets and wildlife, especially when they ingest contaminated water or food sources.

Environmentally, HABs can have devastating effects, as they deplete oxygen levels in water, leading to fish kills and disruptions to aquatic ecosystems. Dense algae blooms can block sunlight and prevent the growth of submerged aquatic plants, which serve as habitat for fish and the organisms they feed on.

Economically, HABs can significantly impact local communities. Beach closures due to unsafe recreational conditions reduce tourism revenue and limit public access to water resources. Fishing areas may be closed when toxins accumulate in shellfish, causing financial losses for coastal industries.

HABs can also threaten drinking water supplies as some toxins can contaminate source waters, requiring advanced treatment methods to ensure safety.

NEIWPCC’s Role in Addressing HABs

In conjunction with our member states and the U.S. Environmental Protection Agency, NEIWPCC continues to address concerns related to HABs and cyanobacteria through our various workgroups, including the Harmful Algal Blooms Workgroup, and at NEIWPCC events. In 2022 and 2024, NEIWPCC hosted the U.S. Symposium on Harmful Algae, bringing together researchers and other professionals from across the country to share their expertise, challenges and solutions.

In 2016, NEIWPCC, EPA Region 1 and CitiSci.org launched a smartphone app, bloomWatch. The app enables community scientists to help document potentially harmful blooms by submitting a photograph and other information from a smartphone or tablet.

For more information, contact Maryann Dugan, coordinator of the HABs Workgroup.

Additional Resources

NEIWPCC State Programs

Advisories