It may have taken over 20 years, but experts have finally traced the source of human waste and cooking fat which has been pouring into a beautiful lake for decades.

Thames Water and the Environment Agency proudly announced this week that their "detectives" have stopped Ewell Court lake from being used as a toilet.

The organisations, dubbing themselves the "dynamic duo", surveyed 2,600 homes, did CCTV surveys and put orange dye into toilets to trace where it flushed.

Fifty-five appliances, including four toilets, were found to be mistakenly connected to the lake.

A Thames Water spokesman claimed the problem was first identified in 2011 but the Epsom Guardian was reporting on the issue back in 2002 when a £100,000 project by the council to clean the lake was thwarted by wrongly connected drains.

Thames Water was surveying homes then and a council spokesman claimed the problem dated back to the 90s.

In November 2007 the pollution got so bad it killed 100 fish.

Councillor Eber Kington, who represents Ewell Court ward, said locals has always been known there are misconnections, with scum from washing machines and cooking oil regularly seen on the lake.

Coun Kington said: "If they are saying they have cracked it at last and it won’t happen again that’s brilliant news for Ewell Court lake and its pond life.

"It’s been a long time coming. Even 20 years ago there were signs this was happening. It has been a long-standing problem."

Les Duplock, chairman of Ewell Court Residents’ Association, said: "We have had residents complain over the years that there was fat and detergent foam on top of the water.

"Nobody knew where it came from. It’s great news that they have tracked it back and found the source."

Of the lake having been used as a sewer for so many years, he said: "It’s despicable, it’s not acceptable at all. It’s really good news that they have sourced it."

Stephanie Ilsley, environment officer at the Environment Agency, said: "The Environment Agency is really pleased that Thames Water’s hard work has helped clean up the flow of polluted water to the lake.

"Sewage and fats were regularly discharging into the watercourse and reducing the water quality for the wildlife and creating an unpleasant environment for visitors to the lake."

A spokeswoman for Thames Water said: "The problem was identified in 2011, and the investigation into the misconnections has been ongoing over the last three years.

"It has now ended as the EA are satisfied that the water quality has improved. All the misconnections identified have been fixed.

"So unless more dodgy builders get to work locally and drains are wrongly connected again, things should be sorted out now!"

Jasmine Killen, from Thames Water’s environment team, said: "The thought of human waste, cooking fat and dirty water going straight into a lake at this beauty spot is frankly disgusting, so we’re really pleased our work here has paid off and we’ve tracked down those homes with misconnected drains."

For more information visit www.connectright.org.uk.