Fears were raised last night that oil particles washed ashore at a north-east beach were spreading up a prominent river.
The estuary of the River Deveron at Banff remained under surveillance yesterday after a clean-up operation to remove oily deposits.
Aberdeenshire Council said small particles were still being picked up, but a local resident claimed more had come ashore.
The oil is thought to have originated from the Beatrice Alpha installation in the Moray Firth, where a spill happened earlier this month.
Operator Talisman Energy (UK) is working with the council and other authorities to monitor deposits and assist in a clean-up.
The company said it would meet all costs associated with the effort.
A Talisman spokesman said it was assumed the oil had come from Beatrice Alpha where a “small spillage” happened on June 3.
Former sub-sea engineer John Gair, 43, of Market Street, Macduff, claimed yesterday oil could now be found in the River Deveron.
He said: “I was fishing just above the bridge this week and you could see the oil in the water, and rushes on the bank were covered in it.
“I think it came in sometime between Wednesday night and Thursday afternoon.
“I am worried about the effects this will have on the environment and on wildlife in the area.”
The Talisman spokesman said: “We can confirm we have deployed a specialist clean-up team to an area of the River Deveron, upstream from Banff, following reports of tar balls in reed beds.”
He said earlier deposits of oil found at the estuary had been cleaned up.
An Aberdeenshire Council spokesman said: “We are still picking up small deposits, particularly at Banff, where they come in due to the nature of the estuary, tides and shingle.
“We are monitoring the situation closely and cleaning up as necessary.”
He said some oil which had washed ashore in the Whitehills area had also been cleaned up.
Two weeks ago, similar deposits were found in the Buckie area, where Talisman also assisted in a clean-up operation. Northern winds in recent days are thought to have driven the oily deposits towards the Moray Firth coastline.