Fort McMurray RCMP arrested 11 Greenpeace activists for trespassing at the Syncrude Canada Ltd. Aurora oilsands site at around 12:30 p.m. MT Thursday.

The RCMP were called after Syncrude employees found the activists at the tailings pond, Const. Ali Fayad said.

The Greenpeace activists were trying to block a pipeline dumping tailings waste into one of Syncrude’s giant tailings ponds.

Organization spokeswoman Jessica Wilson said the activists were detained, handed trespassing tickets carrying a $287 fine and released.

"The action was successful in bringing our message directly to the perpetrators of these environmental crimes," Wilson said.

The environmental group said the action is aimed at stopping the pond, located at the Aurora North Site mine, from growing any larger. It is now about six square km, with 1.8 billion litres of toxic waste added daily, according to Wilson.

Greenpeace activists said they entered the site around 11 a.m. Thursday, and easily got past Syncrude security and made it to the lake of waste water. Wilson said the activists were on site for over an hour before they were noticed.

Dave Martin, who also speaks for the organization, talked to CBC News from the side of the tailings pond.

"It's the pond where 500 ducks were killed in April, and we have another team putting up a banner on another major outflow pipe of tailings. We've got about a 60-foot large-scale banner we are putting up on the sides of the berm," Martin said.

The banner is a giant skull and crossbones, he said, with 'World's Dirtiest Oil: Stop the Tar Sands' on it.

"We're hoping this really sends a message, not only to Syncrude, but to the Stelmach government and the Harper government, to say enough is enough and this has to stop and we have to start caring about our water, climate and about the health of the people that live around here," Martin said.

A Syncrude spokesperson said the Greenpeace action hasn't affected production.

On April 28, about 500 ducks landed on a tailings pond filled with waste from Syncrude's oilsands operation, north of Fort McMurray. Only a handful of birds survived the dip in the toxic water. Most of the ducks were too heavily coated with oil and waste to survive.

Following an investigation, Alberta is still considering whether to charge Syncrude under the province's environmental laws.