Tracking Toxins at the Coastline: A National Look at Harmful Algal Toxins in U.S. Coastal Waters
This study is a major step forward in understanding how harmful algal blooms, which are often associated with lakes and rivers, can also affect coastal environments. It provides important baseline information for scientists, public health officials, and environmental managers.
The U.S. Geological Survey (USGS), working with the Environmental Protection Agency (EPA), carried out a nationwide study to learn more about harmful algal toxins in U.S. coastal and estuarine waters. Using data from the 2015 National Coastal Condition Assessment (NCCA), researchers tested hundreds of water samples to find out whether toxins from algae—both freshwater and marine—were present.
High levels of cyanotoxins and algal toxins were not common in the 2015 samples—all were below the U.S. EPA’s health advisory limits. However, there are no established recreational safety guidelines for domoic acid—a marine toxin that was found in low levels along all U.S. coastlines. This leaves a gap in our ability to assess the risks of exposure through activities like swimming or seafood consumption.
The study analyzed 798 water samples from 732 coastal sites across the U.S., testing for 20 algal toxins using advanced laboratory methods. The results revealed that:
- Domoic acid was the most frequently detected toxin (8.3%), found along all U.S. coastlines—not just the West Coast where it is typically monitored. Because domoic acid can stay in the water, it raises concerns about long-term exposure through seafood, which can lead to serious food poisoning in people—including stomach illness and, in rare cases, memory loss—and can also harm the brains of marine mammals and birds.
- Microcystins were found in 4.0% of samples by ELISA and 2.0% by LC/MS/MS, mostly in low-salinity estuarine waters, suggesting both inland transport and local production. Microcystins are liver toxins that can cause illness in humans through drinking or swimming in contaminated water, can be fatal to pets like dogs that ingest affected water, and may harm fish and aquatic wildlife by damaging liver tissue and disrupting ecosystems.
- Anatoxin-a and cylindrospermopsin were detected less frequently (0.6% and 0.9%), but their presence shows that freshwater toxins are reaching estuarine environments. Anatoxin-a is a fast-acting neurotoxin that can be fatal to pets and wildlife, while cylindrospermopsin can damage the liver and kidneys in both humans and animals.
- Other marine algal toxins were not detected, and mixtures of toxins were rare.
Even though toxin levels were generally low, their presence—even without visible blooms—raises important questions. Domoic acid, for example, can stay in the water in a dissolved form, and scientists don’t yet know how this might affect people or wildlife over time. Cyanotoxins also appear to come from both upstream freshwater sources and from algae growing in the estuaries themselves, making it harder to pinpoint their origins.
Interestingly, the study found that chlorophyll levels—often used as a warning sign for algal blooms—didn’t always match up with toxin levels. In some cases, toxins were present even when chlorophyll was low, and in others, high chlorophyll didn’t mean toxins were there. This suggests that using chlorophyll alone may not be a reliable way to assess toxin risk.
Overall, the study found that while harmful algal toxins were not widespread in 2015, they were still present in many U.S. estuaries and should not be overlooked. The findings point to a clear need for better tools to detect both the algae that produce toxins and the toxins themselves—especially in estuaries, where freshwater and saltwater mix and conditions can be more complex. This research builds on earlier national efforts to monitor toxins in lakes and rivers, and for the first time, extends that focus to include coastal waters.
This study has been supported by the U.S. Geological Survey Ecosystems Mission Area, through the Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and the US Environmental Protection Agency’s National Aquatic Resource Surveys.
This study is a major step forward in understanding how harmful algal blooms, which are often associated with lakes and rivers, can also affect coastal environments. It provides important baseline information for scientists, public health officials, and environmental managers.
The U.S. Geological Survey (USGS), working with the Environmental Protection Agency (EPA), carried out a nationwide study to learn more about harmful algal toxins in U.S. coastal and estuarine waters. Using data from the 2015 National Coastal Condition Assessment (NCCA), researchers tested hundreds of water samples to find out whether toxins from algae—both freshwater and marine—were present.
High levels of cyanotoxins and algal toxins were not common in the 2015 samples—all were below the U.S. EPA’s health advisory limits. However, there are no established recreational safety guidelines for domoic acid—a marine toxin that was found in low levels along all U.S. coastlines. This leaves a gap in our ability to assess the risks of exposure through activities like swimming or seafood consumption.
The study analyzed 798 water samples from 732 coastal sites across the U.S., testing for 20 algal toxins using advanced laboratory methods. The results revealed that:
- Domoic acid was the most frequently detected toxin (8.3%), found along all U.S. coastlines—not just the West Coast where it is typically monitored. Because domoic acid can stay in the water, it raises concerns about long-term exposure through seafood, which can lead to serious food poisoning in people—including stomach illness and, in rare cases, memory loss—and can also harm the brains of marine mammals and birds.
- Microcystins were found in 4.0% of samples by ELISA and 2.0% by LC/MS/MS, mostly in low-salinity estuarine waters, suggesting both inland transport and local production. Microcystins are liver toxins that can cause illness in humans through drinking or swimming in contaminated water, can be fatal to pets like dogs that ingest affected water, and may harm fish and aquatic wildlife by damaging liver tissue and disrupting ecosystems.
- Anatoxin-a and cylindrospermopsin were detected less frequently (0.6% and 0.9%), but their presence shows that freshwater toxins are reaching estuarine environments. Anatoxin-a is a fast-acting neurotoxin that can be fatal to pets and wildlife, while cylindrospermopsin can damage the liver and kidneys in both humans and animals.
- Other marine algal toxins were not detected, and mixtures of toxins were rare.
Even though toxin levels were generally low, their presence—even without visible blooms—raises important questions. Domoic acid, for example, can stay in the water in a dissolved form, and scientists don’t yet know how this might affect people or wildlife over time. Cyanotoxins also appear to come from both upstream freshwater sources and from algae growing in the estuaries themselves, making it harder to pinpoint their origins.
Interestingly, the study found that chlorophyll levels—often used as a warning sign for algal blooms—didn’t always match up with toxin levels. In some cases, toxins were present even when chlorophyll was low, and in others, high chlorophyll didn’t mean toxins were there. This suggests that using chlorophyll alone may not be a reliable way to assess toxin risk.
Overall, the study found that while harmful algal toxins were not widespread in 2015, they were still present in many U.S. estuaries and should not be overlooked. The findings point to a clear need for better tools to detect both the algae that produce toxins and the toxins themselves—especially in estuaries, where freshwater and saltwater mix and conditions can be more complex. This research builds on earlier national efforts to monitor toxins in lakes and rivers, and for the first time, extends that focus to include coastal waters.
This study has been supported by the U.S. Geological Survey Ecosystems Mission Area, through the Environmental Health Program (Contaminant Biology and Toxic Substances Hydrology) and the US Environmental Protection Agency’s National Aquatic Resource Surveys.