Fly-tippers have dumped dangerous waste close to a beauty spot near Wrexham, the Environment Agency has said.
The oil leaking from the drums almost reached a nearby pond
The agency has asked for help in finding whoever left chemical drums, old car parts and office waste at a pond on Eclusham Mountain, Minera.
The drums were leaking engine oil towards a nearby watercourse which supports a variety of wildlife.
A member of the public raised the alert to the fly-tipping which happened late on Monday or early on Tuesday.
Agency staff were said to be horrified at the scale and nature of the rubbish dumped.
The area is a Site of Special Scientific Interest and is of UK and European importance for its wildlife habitats and geological features.
Habitats on the mountain are home to a variety of breeding birds, the limestone grasslands and cliffs hold rare plants and the caves and old mine workings are used by bats.
Environment Agency Wales spokesman Anthony Randles said: "I can't believe there are people out there who show such blatant disregard for the law and the environment.
"This beautiful spot is used by the community all the time and to spoil it all for a quick buck is just plain selfish."
The agency is following-up a tip-off about the fly-tipping as well as evidence found at the scene.
Mr Randles added: "We are determined to take action against anyone operating illegally and putting the environment at risk."
The agency has contacted a specialist contractors to collect and dispose of the waste safely.
Environment Agency Wales has a 24-hour incident hotline on 0800 80 70 60