Ducks and pond life were joined by a strange new neighbour at one of Hampstead Heath’s ponds this week.

A large floating rig was installed on a raft-like structure in the middle of the Model Boating Pond, as part of preparations for the City of London Corporation’s controversial dams project.

The cable suspension rig was set up on Tuesday and will remain for about a week, enabling contractors from engineering firm Bam Nuttall to analyse the pond bed.

The work is part of a 10-week investigation into the Heath’s soil, which will result in 100 holes being bored, ranging from three to 15 metres deep.

The ground survey is aimed at finding out how much on-site earth can be used during the £15million dams project.

The proposed work will raise dams or create new ones at many of the Heath’s 30 ponds, in a bid to stop them overflowing and flooding downstream communities like Gospel Oak and Kentish Town in the event of a catastrophic storm.

A spokesman for the Corporation said: “The ground investigation work will feed into the design process for the ponds project.

“It involves taking small earth samples from the pond dams and surrounding areas – in this case from the pond bed, and laboratory testing them to identify the chemical and physical properties of the different soils below the ground surface.”

She said the floating rig was assembled on site “to reduce the survey’s impact”.

The ponds project is fiercely opposed by the campaign group Dam Nonsense, which says the dams work is unnecessary.

The campaigners have accused the City of carrying out the current ground investigations without any legal authority.

Last week the group welcomed the results of a public consultation, which showed nearly two thirds of people gave the worst possible rating to the proposals.