For 25 years, I've been kayaking the River Thames. I've paddled every glorious mile from the source, just upstream of Lechlade, all the way to the Houses of Parliament and, until recently, held the world record for paddling its length!

Just over 10 years ago, I was kayaking an especially beautiful stretch and saw a for sale sign outside a dilapidated old bungalow. My soon-to-be wife, Helen, and I bought it. We lived at the riverbank on a houseboat for three years and built our dream home there where we intended to bring up our three children.

The Thames is a much more nature-rich river than many might realise. We see kingfisher every day, the grebes court outside our back door, swans have nested in our garden and otter cubs wrestle over eels at night on our deck.

I started teaching the kids to swim in the river during the pandemic when it felt like one big nature reserve. But then things started to go badly wrong.

Four years ago, storm discharges from the Little Marlow sewage treatment works, just upstream of us, started to increase in frequency and severity. There has always been discharges from this plant and Thames Water has had some massive fines in the past, but it was clear that we were seeing something new.

Suddenly 18-hour sewage discharges with brown, churning water pumping stinking effluent out into the river and the local nature reserve were becoming more and more common. Even when the pipe was not discharging, the freshwater outflow stank with the detergent smell of surfactants, and the water came out bubbling with white froth and foam on the surface.

I hooked up with organisation River Action and started testing for phosphate and nitrates in the water. Not surprisingly, these were off the charts and many, many times what they should be in a river like this, however, in my head – as I think in most people’s heads – the problem was the smell, and the prospect of swimming into something very unsavoury.

However in 2023, I was given an honorary senior lecture position at Bangor University. They have a world-class wetlands and waste water centre and wanted to do some scientific research with me. I started the process of a strategic collection protocol upstream and downstream of the treatment works.

There is a part of me that wished I'd never started. When the first results came back it was clear that the folks at the lab thought I might have just been sampling raw sewage. Levels of E. coli, Enterovirus, Norovirus and various phages that you only get in the human gut were here in the river in extraordinary and horrifying levels.

Scientific labs are not given to hysteria, but they refused to even open some of the samples I'd sent as the levels of contaminants were considered a biohazard. They labelled these contaminants as a death potion for the river. My next move was to approach the Environment Agency and Thames Water themselves. To their credit, they were quite open in talking to me but what they had to say was, in many ways, even more horrifying than my results.

It's clear that they were absolutely aware of what they're pouring into the river, and do not consider it a priority to do anything about it. In their words, this is just a normal part of their business. Ofwat, the water regulator, allows them to make these discharges, and, even more shocking, does not force them to screen for viruses and bacteria in their effluent at any time. These contaminant-laden waters are being pumped out into public waterways all the time.

My own tests were being added to a growing consensus from River Action's other willing testers. It seemed that my local treatment plant was by no means the worst now that the word was getting out. It was clear that people were getting sick. Swimmers on our reach had suffered from giardiasis and gastroenteritis, and a few local pet dogs became seriously ill after entering the river.

Before the 2024 Boat Race, a number of rowers had gone down with E. coli and recently, after the Windsor Triathlon, many swimmers reported severe illness following the race. At the same time, I was under increasing pressure from local paddleboard, Scouts, sailing, canoeing and rowing organisations to get back on social media and announce the all clear.

After all, I've spent most of my adult life trying to convince people to get outside to embrace nature, to get involved in outdoor adventure sports, and, all of a sudden, here I was as the voice for telling people to stay out of the Thames!

The big problem was, I was still testing and my tests absolutely did not show that things were getting any better.

My big concern now is substrate. There's no doubt that since our last big discharge in late April, the water itself is clearing. However, my test results show that the sediment on the bottom of the river is still a virulent soup of unpleasant chemicals.

I am still not swimming, and may not for the rest of the year. However, I have started back canoeing and kayaking. The key is to make sure that you wash your hands very carefully after every time being near the river, and to cover up any cuts and grazes,

I hate that I'm writing these words.

I hate that something I've done and said has prevented people from using this magnificent resource that belongs to all of us. But until there are major changes, I absolutely cannot give the all clear. After all, when I asked the Head of Wastewater from Thames Water if he would swim, his response was an incredulous, "well, you wouldn't swim in a sewer, would you?".

So what happens now? We are heading into a general election. At present the only parties who are really vowing to do something big on wastewater are the Greens and the Lib Dems but something big has to change.

The infrastructure we have right now is not sufficient for our present population and climate. As more houses are built (and possibly a big film studios near where I live on the greenbelt) and potentially winter weather gets much, much wetter with climate change, this already overworked facility is going to collapse again and again.

That will be calamitous, for our national river, for the wildlife that depends on it, and for us, the people who value this waterway more than any other.

Ending river pollution is one of The Wildlife Trusts' five priorities for the next government.