Anyone who swims in part of the river Itchen runs a “very severe risk of becoming ill”, a senior Southampton councillor has warned.

Cabinet member for green city and net zero Cllr John Savage was critical of Southern Water, claiming the firm’s investment programme was “very badly lacking”.

Cllr Savage said readings taken earlier this year by the Friends of Itchen Estuary group found the level of E.coli in the water close to St Denys was 34 times greater than what would be acceptable for bathing water status.

Speaking at an overview and scrutiny management committee meeting on Thursday, August 22, Cllr Savage said: “We have three main locations in Southampton for processed sewage to be pushed out into our rivers.

“One is at Millbrook, one is at Woolston and one is at St Denys.

“Woolston and Millbrook both have UV treatment final outflow, so anything that comes out of the sewage works is treated with powerful UV light, which kills bacterial things in the water, but they don’t have that at St Denys and at the moment they are refusing to put that investment in there.

“This means anyone who swims in the St Denys area, Portswood waste water treatment works, runs a very severe risk of becoming ill.”

Most E. coli bacteria are harmless, however, some strains can cause serious illness.

The Labour councillor for Portswood ward said he was concerned the E.coli levels in the river Itchen, particularly around St Denys, were not expressed by an online app available to the public which provided information on the condition of rivers and seas.

He said meetings had taken place with Southern Water, however, hopes of sitting down with the Environment Agency had been delayed by the general election.

“Southern Water maintain that they are operating under the licence agreement, which was agreed in 1976 and perfectly legal in what they are doing and what they are putting in the river according to that licence,” Cllr Savage said

“The reason why we are bringing in the Environment Agency is to re-look at that licence that should have been re-examined over the last 40-odd years.”

There are concerns about the future of wild Atlantic salmon in the area due to the levels of biological deoxygenated water, Cllr Savage said.

Chair of the committee Cllr Richard Blackman said they would formally that they believed there was a need for investment from Southern Water at St Denys.

Cllr Savage said the water company’s next five-year cycle of investment for 2025 onwards was already “sealed”, so any specific project could be many years away.

In a statement to the Local Democracy Reporting Service, John Penicud, Southern Water’s director for wastewater operations, said: “We know we have a big role to play in helping improve the conditions for Atlantic salmon in the river Itchen.

“This is why we’re working closely with the Environment Agency and other key stakeholders to create a coordinated action plan which we hope will make a big difference to the species.

“In addition, we are investing £8m in Portswood Wastewater Treatment Works to improve water quality along this stretch of the river Itchen through introducing a new treatment process and storm tank.

“Lastly, we’re keen to improve our relationship with Southampton City Council and we’re happy to support and work with them on their ambitions for bathing waters and blue spaces at the river Itchen.”