Comedian David Walliams is pressing ahead with his attempt to swim the full length of the Thames despite news that half a million cubic metres of sewage has entered the river in the past week.
The 'Little Britain' star has already battled with a bout of "Thames tummy" from swallowing the river water as he aims to cover 140 miles in eight days.
Thames Water has contacted his team to inform them of the stomach-churning amount of sewage in the water.
Richard Aylard from the water firm said: "We've been in touch with David Walliams' team and he'll have to make his own decisions. We're not public health experts but I wouldn't recommend swimming in it. That said, David is doing a hugely admirable thing and we wish him all the best."
The brave comic, who has had inoculations to protect him against possible diseases during his epic swim, will press on regardless.
Walliams passed the 100 mile mark yesterday in his BT Sport Relief Challenge, spurred on by the presence of his wife Lara Stone in a support boat.
He even rescued a pet Labrador called Vinny that was struggling to get out of the river due to a bad hip.
Walliams said: "I heard a splash and looked over to be met with the face of a sweet Labrador. I thought he was fine, but he started to really struggle when he was getting out so I swam over and helped his owner get him out."
The animal's owner Steve Outten, 23, from High Wycombe, said: "Vinny has hip dysplasia and was really struggling to get out just as David was swimming past. He stopped, swam over and helped me get him out, which when you think what he's going through with the swim is totally amazing, what a man."
Despite concerns that the enormous task could be too much for Walliams, he said today was a "great day" and that having wife Lara in the boat was "such a big boost".
He was also greeted by fellow comic Miranda Hart, who made him porridge for breakfast.
Walliams said: "My tummy has settled a bit and I had fish and chips and some pizza last night so feel better. We have broken through the 100 mile barrier now which is great, but once I reach Teddington Lock the Thames becomes tidal and there's a whole new set of challenges. The currents and undertows are very dangerous so I'll need to be strong."
A spokeswoman for Sport Relief said: "We are working with a reputable, specialist organisation who, whilst planning David's swim, took into account the sewage that enters the Thames following heavy rainfall. They are regularly measuring water quality and are currently reassured that when David reaches the affected areas it will be at an acceptable level.
"In addition, David received a number of inoculations to protect him from disease carried in the Thames and is taking a cause of precautionary antibiotics. A team of medics are with him throughout the swim and are constantly monitoring his health. David's safety has been paramount throughout the course of his swim."
As well as suffering with the stomach bug, Walliams has to undergo physiotherapy at every rest stop during the charity challenge, and he has developed a rash on his neck where his wetsuit has rubbed, which poses a risk of infection.
So far he has raised more than £600,000 (€697,810) and BT is giving £40,000 (€46,520) a day to the fund. Supporters can sponsor the performer at www.sportrelief.com/walliams.
There is also a GPS tracker on the Sport Relief website showing where he is, and a regularly updated Twitter feed.