Raw sewage was discharged into rivers and seas almost 300,000 times last year after the driest spring for more than 100 years and the sunniest and warmest year on record in England.

Water companies released raw sewage into rivers and seas from storm overflows – designed to be used in extreme wet weather conditions – 291,492 times. This was a 35% reduction on record spills in 2024. Average discharges were 20.5 spills for each overflow, compared with 31.8 in the previous year.

The duration of raw sewage discharges into waterways fell by more than half, to 1.8m hours, from a high of almost 4m hours in 2024. Some water companies had reductions of more than 60% and 70% compared with the previous year, according to figures released on Thursday by the Environment Agency (EA).

Despite drought conditions across the country, raw sewage was discharged for almost 1m hours more than in 2018, pointing to the impact of the failure to invest in infrastructure over the long term, campaigners said. However, there were far fewer overflows monitored then.

Raw sewage discharges through storm overflows should happen only in extraordinary conditions, such as very heavy rainfall or storms. In 2025, parts of England were hit by drought for several months and four water companies imposed hosepipe bans.

Richard Benwell, the chief executive of Wildlife and Countryside Link, an umbrella group of 66 environmental charities, said that despite the dry weather, raw sewage was still discharged almost 300,000 times.

“When sewage is pouring out even in a dry year, you really know the system is broken,” Benwell said. “These aren’t stormwater overflows; they’re all-weather waste pipes. Rivers, lakes and seas should not be pressure valves for pollution. Any sewage in our waters is too much.

“This is what systemic failure looks like: multiple sources of pollution, weak oversight and no single body taking responsibility for the health of our waters.”

Michelle Walker, the technical director for the Rivers Trust, said discharging raw sewage almost 300,000 times in drought conditions was in many cases illegal and extremely harmful to the environment and the public.

“We expected to see a lower number of untreated sewage discharges in 2025 as it was such a dry year, but this should not be mistaken for progress,” Walker said. “Far too many of these [discharges] will be happening on dry days and therefore be illegal.

“The impact of those discharges will be even worse when rivers are running low. Each discharge will be more concentrated, more damaging and more dangerous for already stressed ecosystems. At the same time, more people will be taking to rivers and seas to cool down on hot days, putting public health directly at risk.”

The industry acknowledged on Thursday that the dry conditions had contributed to the reductions in raw sewage entering rivers and seas. But water companies said they were also the result of record levels of investment going into the system, after the government imposed targets. An investment of £104bn by water companies is being paid for through increased customer bills, with average bills rising 36% over five years.

Water UK, the industry body, said: “Sewage spills are awful and we are working to end them as fast as we physically can. While the dry weather in 2025 will have led to fewer spills, we are also starting to see the effect of a tripling of water company investment. By building bigger storm tanks and expanding capacity at sewage treatment works, we will halve spills over the next five years.”

The EA said much of the reduction was down to the dry weather and emphasised that sustained maintenance and investment in water industry drainage networks was needed to bring lasting improvements.

The water minister, Emma Hardy, said: “It is good to see that storm overflow spills are down since the previous year, but there is still an unacceptable amount of sewage entering our waterways and a long way to go in cleaning up our rivers, lakes and seas.”

In Yorkshire, where the water company was downgraded to a two-star performance as a result of increased pollution incidents, the summer was so dry that a hosepipe ban was imposed for five months.

Karen Shackleton, of Ilkley Clean River Group, said: “Today’s report creates a cover for water companies’ illegal pollution and neglect of our infrastructure. The figures for last year, in drought conditions, take us back to the level of pollution we had two to three years ago in normal weather. This is not a good news story. Yorkshire Water is still polluting illegally and the government is still failing to hold them to account.”

South West Water, with 860 miles (1,380km) of coastline, discharged raw sewage for the longest period, 407,000 hours, in 2025, followed by United Utilities (327,000 hours) and Yorkshire Water (285,000 hours).

Thames Water, which has been on the brink of collapse for more than two years as it struggles under the weight of £17.6bn in debt, discharged raw sewage for 107,000 hours.

A South West Water spokesperson said: “The South West saw 62% more rain than the rest of England in 2025. Despite this, we still cut storm overflow spills by 17% and spill duration by 25%.

“We also prevented more than 8,300 spills, due to operational improvement, with a focus on beaches during bathing season – a clear sign our £760 million investment plan is already producing strong results. There’s more to do, but the direction is clear: fewer spills, shorter durations, and investment where it matters most.”