What is blue-green algae and why is it such a problem?

Long-term pollution – largely from agriculture – is a key part of the problem.

Run-off of fertiliser from surrounding fields over many decades has increased the nutrients in the water, feeding the bacteria’s growth.

Along with invasive species in the form of water-clearing zebra mussels, the effects of climate change on water temperature in the lough and on our weather help create the perfect conditions for the potentially toxic algae to bloom from the depths where it has always been present.

Dr Matthew Service, from the Agri-Food and Biosciences Institute (AFBI), said blue-green algae spreads rapidly.

“It starts to double every seven to 14 days,” he said.

“So once you get to where you can see it, it’s just going to keep going until either the climatic conditions change, there’s not enough light for it to reproduce or it just simply breaks up with the autumn and winter weather.”

Again this summer, AFBI scientists have detected the algae out in the middle of Lough Neagh, showing the wind is moving the very buoyant species around and causing it to clump together – or aggregate.