The secret transfer of Russian fuel cargoes between tankers at sea has shifted to new locations off the coast of Greece, according to a Bloomberg report.

Approximately 1 million barrels of diesel, fuel oil, and other petroleum products are being transferred monthly near Lesvos and Chios in the Aegean Sea, as per data from the analytics company Vortexa. This area gained prominence only after the Greek Navy conducted exercises around the Laconian Gulf, which had previously been Europe’s top location for this practice.

The increase in ship-to-ship transfers of Russian oil and fuel in and around Europe has raised environmental concerns, with questions arising over the safety and insurance of the involved vessels.