Target: halve spills from storm overflows by 2030, from the 2024 average of 31.8 per overflow to 15.9 (Environmental Improvement Plan 2025). The straight path needs 29.2 by now. Spills rise and fall with rainfall, so one dry year can put the figure ahead of the path.

What it means: storm overflows release diluted sewage into rivers and the sea when sewers are overwhelmed, usually after heavy rain. The figure is the average number of spills recorded per monitored overflow. It swings with rainfall: 2025 was unusually dry after a wet 2024. A change of two spills or more counts.

Source: Environment Agency, storm overflow event duration monitoring, annual releases for 2023 to 2025 (2021 not published in the same form).