Submarine plow PL3 arrived in the Baltic Sea to dig a trench for the Nord Stream pipeline in Swedish and Danish waters.
Russian energy company Gazprom is leading the project consortium building the dual natural gas pipeline from the Gulf of Finland through the Baltic Sea to Germany. The project is meant to diversify Gazprom's export options as about 80 percent of Russian gas for Europe travels through Ukraine currently.
Environmental groups complained the dual pipeline would have negative consequences, though the consortium said its models show that subsurface plowing wouldn't create environmental problems.
The consortium last week announced that it completed two of the three sections of the first line of the natural gas pipeline. Engineers will finish the third leg by April.
The cost of the pipeline is around $10 billion. Once both lines are completed, which is expected in 2012, it will be the most advanced and environmentally friendly of major pipelines for the European community, the consortium said.