Boaters in Hackney have been told not to move their vessels as environment bosses work to clean up a major oil spill polluting the Lea.

Waterways are shut between Stonebridge Lock just north of Tottenham and the bottom lock of the Hertford Union Canal in Hackney Wick. Both sets of gates are locked.

The Canal and River Trust this week told boaters to stay put to avoid spreading the oil. Continuous cruisers, whose licences normally require them to change moorings every fortnight, have been given leave to remain where they are for the time being.

The pollution is thick, black and described as “acrid”. Boaters and animal welfare workers believe it could be waste engine oil.

It is not yet known where the spill originated. The Environment Agency has now been investigating for 10 days.

Swan Sanctuary volunteer Gill Walker said yesterday the charity had rescued 15 swans from the water – and that 40 others needed treatment following a spill in the same area less than two months ago.

“Whatever this is – it’s certainly got a lot of diesel in it – it gets onto their skin and it’s corrosive,” she said.

“And where they’re constantly preening, it’s getting into their digestive systems and they are constantly exposed to it.

“It isn’t just what you see. The oil strips them of their natural waterproofing, which makes them waterlogged, and spoils their insulation [so even in warmer temperatures] they can suffer from hypothermia.”

The Canal and River Trust is holding community clean-ups from 10am to 2pm tomorrow, Thursday and Friday.

Volunteers can meet at the Lee Bridge Weir and Old Ford at 10am. The groups will be briefed and will work their way toward each other.

“The event will be from the towpath and working on the smaller spills in between boats,” said a spokesman. “People are advised to wear old clothes.”

If you want to take part, you are asked to e-mail enquiries.london@canalrivertrust.org.uk

The Environment Agency said in a statement: “Environment Agency officers have been working alongside specialist contractors and the Canal and River Trust to clear up the oil pollution.

“To date, this oil pollution has been spotted over a 7km stretch of the River Lea affecting both the watercourse and local wildlife. Boat traffic debris and the wind are complicating the clean-up process. However, booms are in place to enclose the oil and the Canal and River Trust have closed some locks to help contain it as much as possible.

“We are aware of concerns over health and safety and advise river users and members of the public to contact Public Health England for help and information. The Canal and River Trust has been offering absorbent material to boat owners, to use near their boats.

“At this point our investigation is still ongoing and we will continue to work to clear up the oil, monitor the watercourse and investigate the cause of the pollution. We encourage members of the public with any information on this to report it to our incident line on 0800 80 70 60.”