Sewage and storm water was poured into the Thames for 20 hours earlier this week following discharges from the Mogden works.

Overflows from tanks at the giant sewage treatment works ran from 5am on Monday morning through to 1.15 am on Tuesday morning.

This the latest in a number of sewage releases from Mogden into the Thames at a point on the Isleworth bank of the river – around Isleworth Ait - opposite the Old Deer Park.

As a result, Thames Water, which runs Mogden, stated: "This means there could be sewage in this section of the watercourse."

The Isleworth Ait island is described as an undisturbed sanctuary for birds, beetles and rare molluscs by the London Wildlife Trust, which has managed it as a reserve since 1995.

There have also been recent releases of sewage from a treatment plant in Hammersmith and another from storm overflows in Petersham.

The releases come against the background of increasing numbers of people using the river for wild swimming, even during the winter, as well as rowing, canoeing and paddle boarding. Problems stem from the fact Mogden cannot cope when there are prolonged periods of rain.

The most recent release from Mogden came at the same time as Thames Water was holding a public consultation in Richmond over controversial plans to take millions of litres of water a day from the river at times of drought and replace it with treated sewage effluent from Mogden.

This scheme will involve building a new 15km pipeline from Mogden to the Thames at a point upstream of Teddington Weir.

Discharges from Mogden have polluted Duke of Northumberland river in the past and led to the flooding of nearby streets.

MPs, environment and river clean-up campaigners have slammed Thames Water for its failure to protect rivers, wildlife and the public by allowing huge quantities of sewerage to be released into the Thames.

They have accused the government of allowing water companies to get away with mass pollution. At the same time, MPs say the ability of the Environment Agency to police sewage discharges has been gutted by 10 years of budget cuts.

Thames Water argues that a new sewage outfall mapping system, which can be viewed by the public, is part of a guarantee greater transparency about its activities.

Thames Water said: "Taking action to improve the health of rivers is a key focus for us, but we also need to explain what is happening, and why.

"After a successful trial in the Oxford area, we have decided to provide close to real-time information about storm discharges from all of our 468 permitted locations. This is a key part of our River Health Action Plan to radically improve both performance and transparency in order to protect and improve the environment.

"We are absolutely committed to protecting and enhancing our rivers and the communities who love them."

The sewage discharge map can be found here – https://www.thameswater.co.uk/edm-map