It is the "smell of decay and death", says Beth Stauffer, from the University of Louisiana. "It has a physical presence. This layer of very striking greens and blueish greens…when you put your paddle in it, you can feel it."
She's describing the harmful algal blooms (HABs) that used to be more associated with marine environments. But in recent years they've been moving further inland and affecting freshwater systems, too. And scientists such as Stauffer are trying to find out why.
HABs occur when certain kinds of algae grow very quickly due to increased nutrients in the water – typically when artificial nitrogen and phosphorus applied to farmers' fields wash out in the rain and enter waterways. The algae receive a meal on a scale they would never get naturally, and a bloom is formed. Sometimes this is harmless. But at scale, many types of algae can turn toxic and harmful to humans and animals. And this scale can be extraordinary.
The explosive growth of algal blooms is linked to rising temperatures and rising pollution. These green waves are both a warning sign and a symptom of a changing climate. As farming fertiliser and a tsunami of human sewage hit our warming waterways, we are in danger of turning our very drinking water toxic.
Farming fertiliser and sewage pollution is turning drinking water toxic (Credit: Yuliia Zozulia / Getty Images)
According to an overview of HABs by the binational United States and Canada Great Lakes organisation The International Joint Commission, only 12 published accounts of algal outbreaks were recorded in Canada and the US in the 1980s and just 19 in the 1990s. By the mid-2000s, however, reports of HABs suddenly began appearing in unlikely landlocked states. By 2021, nearly 1,700 HAB-related warnings and public health advisories were issued within the US alone. HABs are now a major environmental problem in all 50 states.
These toxins may also be entering the food chain. In August 2022, over 60 California sea lions showing signs of domoic acid intoxication – including seizures, disorientation and loss of muscle control – had to be saved following an HAB incident. Stauffer confirms that this now occurs annually on the western and eastern coasts of the US. "Sea lions aren't feeding on little microscopic [organisms], they're feeding on fish, on crustaceans," she says, just like we do. Sea lions commonly feed on fish such as anchovies. During the 2015 incident, anchovies caught in fishing nets were found to have very high levels neurotoxins from the algal blooms.
This is far from a US-only problem. Jessica Richardson, a researcher at the Centre for Ecology & Hydrology, Lancaster Environment Centre in the UK, has described blooms of cyanobacteria as a "threat to global water security" that is expected to increase due to a chemical and climate cocktail of "nutrient enrichment, increasing temperature and extreme precipitation in combination with prolonged drought". In short, more sewag
According to an overview of HABs by the binational United States and Canada Great Lakes organisation The International Joint Commission, only 12 published accounts of algal outbreaks were recorded in Canada and the US in the 1980s and just 19 in the 1990s. By the mid-2000s, however, reports of HABs suddenly began appearing in unlikely landlocked states. By 2021, nearly 1,700 HAB-related warnings and public health advisories were issued within the US alone. HABs are now a major environmental problem in all 50 states.
These toxins may also be entering the food chain. In August 2022, over 60 California sea lions showing signs of domoic acid intoxication – including seizures, disorientation and loss of muscle control – had to be saved following an HAB incident. Stauffer confirms that this now occurs annually on the western and eastern coasts of the US. "Sea lions aren't feeding on little microscopic [organisms], they're feeding on fish, on crustaceans," she says, just like we do. Sea lions commonly feed on fish such as anchovies. During the 2015 incident, anchovies caught in fishing nets were found to have very high levels neurotoxins from the algal blooms.
This is far from a US-only problem. Jessica Richardson, a researcher at the Centre for Ecology & Hydrology, Lancaster Environment Centre in the UK, has described blooms of cyanobacteria as a "threat to global water security" that is expected to increase due to a chemical and climate cocktail of "nutrient enrichment, increasing temperature and extreme precipitation in combination with prolonged drought". In short, more sewag
According to an overview of HABs by the binational United States and Canada Great Lakes organisation The International Joint Commission, only 12 published accounts of algal outbreaks were recorded in Canada and the US in the 1980s and just 19 in the 1990s. By the mid-2000s, however, reports of HABs suddenly began appearing in unlikely landlocked states. By 2021, nearly 1,700 HAB-related warnings and public health advisories were issued within the US alone. HABs are now a major environmental problem in all 50 states.
These toxins may also be entering the food chain. In August 2022, over 60 California sea lions showing signs of domoic acid intoxication – including seizures, disorientation and loss of muscle control – had to be saved following an HAB incident. Stauffer confirms that this now occurs annually on the western and eastern coasts of the US. "Sea lions aren't feeding on little microscopic [organisms], they're feeding on fish, on crustaceans," she says, just like we do. Sea lions commonly feed on fish such as anchovies. During the 2015 incident, anchovies caught in fishing nets were found to have very high levels neurotoxins from the algal blooms.
This is far from a US-only problem. Jessica Richardson, a researcher at the Centre for Ecology & Hydrology, Lancaster Environment Centre in the UK, has described blooms of cyanobacteria as a "threat to global water security" that is expected to increase due to a chemical and climate cocktail of "nutrient enrichment, increasing temperature and extreme precipitation in combination with prolonged drought". In short, more sewag
SENSORY OVERLOAD
From the microplastics sprayed on farmland to the noxious odours released by sewage plants and the noise harming marine life, pollutants are seeping into every aspect of our existence. Sensory Overload explores the impact of pollution on all our senses and the long-term harm it is inflicting on humans and the natural world. Read some of the other stories from the series here:
The underwater sounds that can kill
Why you are probably eating plastic
Harmful algal blooms are a major environmental problem in all 50 US states (Credit: Alamy)
he Windermere algal bloom peaked this summer on 13 August, photographed by satellite covering half the lake and reaching from bank to bank. "A video taken from 14 [August], which I put up on social media, shows a little girl swimming in amongst this blue-green algae. It's such an incredible threat," says Staniek, adding that several people have contacted him to say they became ill, mostly with vomiting and diarrhoea, after swimming in the water.
Great Lakes, great blooms
The blooms on the American Great Lake, Lake Erie, however, are arguably the world's worst, known to cover an area the size of New York City. In 2014, a major HAB on Lake Erie, the world's 11th largest freshwater lake, prompted the city of Toledo, Ohio, to issue a "do not drink" order for tap water that affected nearly 500,000 people for three days. Residents couldn't even use the water to brush their teeth. More than 100 fell sick, becoming the country's first recorded drinking water–associated public health outbreak caused by harmful algal blooms.