People are being warned against going into a river in West Lothian after vandals caused 2,000 litres of diesel to spill into the water.
The Scottish Environment Protection Agency (Sepa) said extensive pollution had been caused in the River Almond.
The source of the leak is a vandalised diesel tank in the derelict Buchanan House on Kirkston Road North, the former EDS print centre in Livingston.
Gallons of fuel fed into the river before it was stopped on Wednesday.
Simon Cole, a senior Sepa officer, said "extensive pollution" of the River Almond had occurred.
He said: "A clean up operation is now under way to try to minimise the impact on the surrounding environment.
"Diesel is being sucked out of the drains on site, and booms have been laid over the tributary of the Almond.
"Our officers are remaining on site to continue their investigations and are liaising with West Lothian Council's environmental health officers and the SSPCA, who are concerned about the river's wildlife."
West Lothian Council's executive councillor for the environment, Robert De Bold, added that it was "strongly advised" that neither people nor dogs should enter the water.
The River Almond is 28 miles (45 km) long, rising in North Lanarkshire near Shotts and running through West Lothian, draining into the Firth of Forth at Cramond near Edinburgh.