Greenpeace activists dumped the first of about 150 three-ton granite slabs into the North Sea off Germany on Tuesday, an effort meant to deter bottom trawling and protect a reef.
"Fishermen won't be very happy to have a three-ton stone in their nets," said Thilo Maack, a spokesman for the group, which set sail from Hamburg early Tuesday for the Sylt Outer Reef with three ships and several inflatable rafts about 40 miles off the coast.
The reef is a European Union-designated conservation area but also, Greenpeace says, used for commercial fishing by boats that trawl the sea floor with nets. That has resulted in the destruction of numerous fish and other species, said Greenpeace Germany member Iris Menn.
The slabs were being tossed overboard in a bid to obstruct the nets used for bottom trawling and to make it harder for sand and gravel to be extracted from the sea floor.
"We managed to drop about 40," Menn said, adding that strong wind and bad weather had forced the Noortland and the other ships and rafts to return to port. She said they planned to head back out again this week to drop the rest of the rocks.
Maack said the stones could also create new habitats for the area, which is a breeding ground for the North Sea dolphin and home to one of the last remaining reefs in the North Sea.
The German Environment Ministry said it takes wildlife protection very seriously. However, a European Union initiative named Natura 2000 to establish marine conservation reserves "does not mean to ban all economic activities," ministry spokesman Thomas Hagbeck said.
Maack contended that the program offers "just paper protection ... no protection from our perspective, no protection at all."
He said Greenpeace kept its boats within German waters, but is mulling a similar operation in neighboring Denmark and in British waters.
"We don't want to wait any longer," he said.