Activists say creditors of the water company have proposed a deal that would allow pollution outside legal limits for up to 14 years as part of ongoing financial restructuring talks.
The agreement had been expected to conclude at the end of 2025, but discussions are continuing.
Campaigners argue the proposal would amount to “pollution for profit” and are urging regulators and ministers not to approve it.
On Wednesday, March 4, protesters will gather near the Rye Dyke to demand the Government reject what they describe as “illegal Thames Water pollution until 2040”.
Organisers say they plan to bring 14 giant inflatable poo emojis – one for each year they claim the deal would allow sewage discharges beyond legal limits.
They say: “Ofwat and this government are struggling to sign off on it because brilliant protestors like you have highlighted just how scandalous it is. We need to keep to keep the pressure on.
“We’ll be in the heart of Environment Secretary Emma Reynolds’ constituency, telling her that she must say NO to illegal Thames Water pollution until 2040.
“We’ve got 14 giant inflatable poo emojos – one for every year of sewage that this deal would be signing off on.
“We’re taking them to the banks of the Rye Dyke, so we can highlight just how disastrous this deal would be for our rivers and seas.
“The more people that gather to protest, the stronger our message: we won’t accept pollution for profit.”
The demonstration is due to take place from 12pm to 1pm outside the Boathouse Café on Wendover Way, near the Rye Dyke in High Wycombe.
Thames Water has been contacted for comment.