Swim relay repeatedly hindered by polluted waters

The eight swimmers eventually reached Westminster, where they called for "urgent action" to protect the UK's waters

Eight swimmers who attempted a 200km (124-mile) relay along the length of the River Thames say they could not swim stretches of the route because of water pollution.

The participants, coordinated by Surfers Against Sewage (SAS), set off on Monday from Lechlade, Gloucestershire, and finished at Teddington Lock on Thursday.

They then travelled by boat and kayak to Westminster, where they called for "urgent action to protect the UK's rivers, lakes, and seas".

SAS chief executive Giles Bristow said: "The fact that citizen scientists found E. coli levels so high that the athletes could not safely swim through Henley shows how dangerous this crisis has become."

The swim featured athletes from all four nations of the UK navigating through Gloucestershire, Oxfordshire, Berkshire, Buckinghamshire and Surrey.

SAS tracked pollution in the Thames during the challenge, monitoring E. coli, ammonia and oxygen levels.

The group planned to swim the relay continuously over the four days but were forced to travel parts of it by boat.

SAS said there were high levels of E. coli at Henley-on-Thames and near Little Marlow sewage treatment works, and discharges near Old Windsor and Chertsey.

Amber Keegan said parts of the river were "absolutely disgusting"

The challengers travelled the final part of the route by boat and kayak

The swimmers included two-time world champion Amber Keegan, Olympians Toby Robinson and Hector Pardoe, and ultramarathon swimmers Jessika Robson and Daniel Smyth.

Ms Keegan said: "This was one of the toughest challenges I've ever taken on, but what shocked me most wasn't the distance or the fatigue, it was the state of the water."

She said some points along the river were "absolutely disgusting".

"Nobody should have to risk their health just to enjoy their local river. It's 2025, and this simply isn't acceptable."

Mr Maclean called it a "tough week that tested us all".

He added: "The fact we literally couldn't swim the full route proves our point, and I hope one day an uninterrupted Thames relay will be possible."

The swimmers represented the UK's four nations

Thames Water, which was recently granted permission to pay its record fine of £122.7m in instalments, described "clean, safe rivers" as a "shared priority", and said it supported efforts that raised awareness and drove improvements in water quality.

It said it was addressing its "ageing infrastructure" with £9.5bn of investment towards its wastewater assets.

A Defra spokesperson said: "This government has put in place the building blocks to clean up England's rivers, lakes and seas for good.

"We have reset the industry, with new laws to block bonuses for 10 polluting water executives.

"Now we are going further, investing over £104bn of private investment to upgrade crumbling pipes and halve sewage pollution by 2030."

Campaigners tracked pollution in the Thames during the challenge