Blue-Green Algae Returns to Lough Neagh

Blue-green algae has been detected in Lough Neagh, marking the first occurrence this year. Verified sightings were reported on the south-west shore, with other instances noted in County Tyrone and County Down in early 2026. Although recent stormy and cool weather has hindered its proliferation, the algae is expected to surge with warmer conditions. High nutrient levels, primarily phosphorus and nitrogen from agricultural runoff, wastewater, and septic systems, are the main drivers of its growth.

The presence of invasive zebra mussels has significantly altered the lough's ecosystem. These mussels consume native algae but avoid the toxic blue-green variety, leading to clearer water and less competition for nutrients. Furthermore, climate change has contributed to an observed increase in Lough Neagh's temperature by at least one degree Celsius since 1995, creating a more favorable environment for algal blooms.