Video report from ITV News Meridians Charlotte Briere-Edney
New information, obtained by ITV News Meridian, reveals that raw sewage was released into our rivers for hundreds of thousands of hours last year.
The figures illustrate the scale of a problem that the water industry has admitted will take "a generation" to fix.
Campaigners have spent years lobbying Thames Water, asking it to clean up its act. The company has, now, pledged publicly to do so.
It's a problem that lurks beneath the surface. Sanitary waste stuck to the riverbed. Brown sludgy growths, known as sewage fungus, are widespread.
The above footage was shot at Colwell Brook in Witney by Ash Smith, who's been measuring the impact of raw sewage being released into our rivers, and campaigning against it.
Ash Smith, Campaigner
He says: "It's quite stunning really. At the beginning of this, we were told and we believed that spilling into our rivers happened for short periods, like a few hours, that it was in extreme events, storm events".
"Well that's not the case."
Ash continues: "Now we're seeing it happen so frequently, and in some places, for such long periods, that it can't be justified, nowhere near can it be justified. It's made it profitable to pollute."
Water companies treat sewage from our toilets and rainwater also gets into the system. So after bad weather, and to avoid sewage backing up into our homes, excess can be released into rivers.
It's supposed to only happen in very wet conditions.
But the figures obtained by ITV News Meridian show that last year, across its network of hundreds of treatment plants, Thames Water spilled sewage into waterways for some 215,000 hours.
That's the equivalent of about 24 years of continuous discharge.
Equivalent of time sewage released for
Most of the time, this is legal. In 2019, Thames Water told ITV News Meridian that sewage spillages were "undesirable" but happen when there's "literally no alternative".
Now, they've promised to invest and reduce discharges.
Alex Saunders, Regional Operations Manager, Thames Water
The Regional Operations Manager at Thames Water, Alex Saunders, says: "I think the really important point is that we at Thames Water don't think it's acceptable. We have a system, like everywhere in the country that's designed that way".
The cash will pay for works like this, relining sewer pipes to prevent groundwater seeping in through cracks. And bigger projects too, like upgrades to the sewage plant at Witney which will increase its treatment capacity by a third.
Climate change and increasing populations will continue to put pressure on the network. There's simply no quick fix.
Alex Saunders says: "This is not something where it's just a plan for the future. We're investing right now, but it is going to take a generation. But we're up for the challenge"
The hope is now, things will start to get better, and in years to come our waterways will be cleaner.