Finland approved the pipeline last month, and the pipeline’s operator started preparatory work shortly after that.

The work involves detonating World War Two bombs on the sea floor along the pipeline’s proposed route and ClientEarth said that could cause serious harm to porpoises, seals, and birds.

A Nord Stream spokeswoman said the project organisation would examine the complaint, but added that it had agreed with Finnish authorities on mitigation measures to reduce the impact on marine life.

The proposed pipeline between Russia and Germany, owned by Russian gas export monopoly Gazprom, is set to cross around 375 kilometres of Finland’s economic zone through the Baltic Sea.

Like Finland, Germany has also approved the pipeline. The project is currently collecting permits from Russia, Sweden and Denmark.