Blue-Green Algae Is Filling Rivers With Toxic Sludge

This year in Northern Ireland, some of the most serious blooms have occurred in Lough Neagh, the largest body of fresh water by surface area in the UK and Ireland. Some locals have described algal blooms on the lough as the worst they have seen in their lifetimes, and there have been reports of multiple dog deaths possibly caused by cyanotoxins. From Lough Neagh, water flows into the River Bann and heads north toward the town of Coleraine, where Rob Skelly’s water sports business was located until recently. Finally, the Bann enters the sea on the north coast of Northern Ireland. Warnings about blue-green algae were put up on beaches there earlier this summer.

WIRED showed Paerl pictures of a blueish residue above the waterline at a jetty very near to Lough Neagh. “It’s an indication of very high amounts of material,” he says.

Around 40 percent of all Northern Ireland’s drinking water is sourced from Lough Neagh. NI Water, the public body responsible for drinking water, says it uses methods known to remove cyanotoxins. Chlorination alone is not enough, notes Paerl. In 2007, a blue-green algal bloom at Lake Taihu in China was so severe that 2 million people were forced to go without drinking water for at least a week.

A spokeswoman for NI Water says that drinking water is treated using granular activated carbon, a kind of filtration that removes certain chemicals, including cyanotoxins. Tests for one particular cyanotoxin, microcystin-LR, in drinking water post-treatment have consistently shown extremely low levels throughout 2023, well below World Health Organization guidelines, she adds.

However, NI Water does not test for cyanotoxins in the source water. “To the best of my knowledge, no one has yet tested for toxins either in water or fish,” says Matt Service at Northern Ireland’s Agri-Food and Biosciences Institute. Some local scientists are concerned that our understanding of how abundant these toxins are in places like Lough Neagh remains very murky.

“I was interested in whether I could get some funding to specifically study the toxicology of the blue-green algae,” says Neil Reid, a senior lecturer in conservation biology at Queen’s University Belfast. He has collected multiple samples of surface water but hasn’t yet been able to secure the funding needed to conduct research on them.

Reid points out that quite a lot of the visible sludge could be a harmless species of algae and not the dreaded cyanobacteria. It would help local people understand the risk when fishing on the lough, for example, if they knew more about its toxicity, he suggests. But, for now, the samples will remain frozen in a laboratory freezer.

Besides nutrients entering lakes and rivers, which can spur the proliferation of algae and cyanobacteria, there are other factors that can trigger major blooms. Northern Ireland just had its wettest July on record—potentially accelerating the runoff of nutrients into bodies of water including Lough Neagh, says Reid. The lough is also 1 degree Celsius warmer today than it was just 30 years ago. That could benefit cyanobacteria over competing species, including algae, says Don Anderson, a senior scientist in the biology department at Woods Hole Oceanographic Institution in Massachusetts.