In freshwater environments, such as lakes and reservoirs, cyanobacteria (blue-green algae) release toxins that trigger harmful algae blooms and lead to algae-associated illnesses. These single-celled microscopic organisms, known as phytoplankton, pose a serious risk to human and animal health. However, when these algae manifest and produce harmful algal bloom toxins, exposure can cause human and animal illnesses.
How people are exposed to harmful algae toxins
In regions with blue-green algal blooms, recreational exposure tends to occur while swimming, fishing, or boating. Swallowing water contaminated with harmful algal bloom toxins, skin contact with smelly water, eating toxic shellfish or fish from contaminated salt water or fresh water, and inhaling toxic aerosols or airborne droplets can all serve to irritate the lungs, skin, eyes, nose, and throat, causing respiratory symptoms, skin rashes, sore throat, and other adverse health effects.
In the U.S., water suppliers must treat, disinfect, and monitor their customers’ drinking water to prevent human and animal illnesses caused by harmful algae. When officials detect toxic algae or other contaminants in drinking water, local governments issue warnings advising residents not to drink tap water or use it for cooking. However, in 2014, in Ohio, more than 500,000 Toledo residents were left without safe water due to toxic algae in the city’s water supply, which was caused by a harmful algal bloom in Lake Erie. This event remains one of the most notable modern examples of algae-associated illnesses, highlighting the risks harmful algal blooms pose to public health.
Meanwhile, drinking or eating seafood such as fish or shellfish from contaminated waters can result in more severe symptoms caused by gastrointestinal symptoms, including stomach aches, abdominal cramps, incapacitating diarrhea, vomiting, headaches, neurological symptoms, abdominal pain, and short-term memory loss.
Illnesses linked to algae toxins
A recent University of South Carolina study has identified a link between microcystin, a harmful algal bloom toxin produced by blue-green algae, and neurological dysfunction as well as neurological disorders affecting the nervous system. Additionally, the findings suggest that people with liver disease are more prone to neurological problems if exposed to toxic algae blooms.
So, seemingly, the algal toxins and liver disease go hand in hand. According to the study, an opening in the barrier around the brain allows “inflammation-causing chemicals or molecules” to travel between the liver and the brain, potentially triggering neurological symptoms and other health effects. The damage caused by algae toxins to the liver might lead to liver damage, hepatic failure, liver cancer, and ultimately death if not immediately treated with proper medical treatment by a healthcare provider.
In 2021, researchers discovered a toxin called anatoxin-a (ATX) in the air near an algae-contaminated lake. Through extensive testing, they proved that this harmful algal bloom toxin can cause loss of coordination, respiratory difficulty, respiratory arrest, or even death in humans and animals. Researchers also discovered that the toxin spreads easily through the air, infecting people who inhale particles near contaminated water bodies. This finding highlights the serious risk harmful algal blooms pose to human and animal health.
Public health concern and regulatory response
In the United States, all 50 states, as well as Puerto Rico and the U.S. Virgin Islands, have reported freshwater cyanobacterial blooms, a type of harmful algal bloom that can produce toxins known as harmful algal bloom toxins. In October 2021, NASA reported detecting cyanobacteria in more than 2,300 lakes across the United States, contaminating surface waters including lakes, reservoirs, and rivers. Meanwhile, 85% of the U.S. population receives water from municipal water suppliers, relying on these surface waters, including fresh water and brackish water, as their primary drinking water source.
In recent years, increasing numbers of water suppliers have shifted to a multi-barrier approach for drinking water, designing processes and utilizing technologies to reduce contamination from harmful algal bloom toxins and lower public health risks. This approach helps prevent algae-associated illnesses caused by exposure to algal toxins, protecting people and animals from severe health effects such as gastrointestinal and neurological symptoms. The Centers for Disease Control and disease control agencies monitor toxin levels to ensure safe water quality and reduce risks associated with harmful algal blooms and their toxins.
Regulatory pressure is intensifying alongside the science. The US EPA has established health advisories for microcystins and cylindrospermopsin in drinking water. The WHO has published guideline values for microcystins in drinking water and recreational water. Water utilities operating on bloom-prone source waters face growing compliance requirements that make early detection and prevention not just operationally desirable but legally necessary.
How water utilities can reduce public health risk
Treating cyanotoxins at the water treatment plant is technically feasible but costly, operationally demanding, and not always fully effective — particularly during severe bloom events when toxin concentrations spike rapidly. The more reliable and cost-effective strategy is preventing blooms from reaching critical concentrations in the first place.
This requires continuous monitoring of source water conditions — tracking the parameters that drive bloom development (temperature, nutrient levels, dissolved oxygen, chlorophyll a) before a bloom fully forms. Early warning systems that alert operators to deteriorating conditions allow intervention while treatment is still manageable.
LG Sonic’s Monitoring Buoy provides continuous real-time measurement of key water quality parameters, with threshold alerts delivered directly to operators. Where active bloom control is required, the MPC-Buoy combines monitoring with targeted ultrasonic treatment — disrupting cyanobacteria growth without chemicals or harm to other aquatic organisms.
Protecting public health from algae-associated illnesses begins at the source. The earlier an emerging bloom is detected and addressed, the lower the risk it poses to the communities that depend on that water.
Managing a drinking water reservoir or recreational lake affected by algal blooms? Contact our team to discuss monitoring and early intervention options.