Declan Coney, a former eel fisher, knew there was something wrong when the famed swarms of Lough Neagh flies failed to materialise. In past years, they would appear around the Northern Irish lake in thick plumes and “wisps” – sometimes prompting mistaken alarm of a fire incident, Lough Shore residents say.
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Last spring the flies never arrived. “This is the first year ever that, if you walked up to the Cross of Ardboe or the area around there, you’d find there’s no flies,” Coney says.
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“Lough Neagh fly” can refer to various non-biting midges, but these crucial insects support fish and wildfowl that are endemic to the lough system, as well as frogs and predatory insects. The loss of these keystone species, alongside sharp reductions of others, the spread of invasive species like zebra mussels, and a long-term deterioration in water quality, indicates deep trouble across the lough’s entire ecology. It also raises the prospect that this shallow body of water and its surrounding wetlands may have shifted beyond a state of decline into cascading ecosystem collapse.
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Last summer, a vast “bloom” of blue-green algae – a thick, photosynthesising blanket that deprives the lake of oxygen, choking aquatic life – brought the lough’s accelerating biodiversity crisis into sharp focus. It prompted considerable public outcry and is expected to return in “more severe” form this coming summer.

https://www.theguardian.com/environment/2024/feb/19/like-the-flip-of-a-switch-its-gone-has-the-ecosystem-of-the-uk-largest-lake-collapsed-aoe