At a time when the eight NATO nations bordering the Baltic Sea are on high alert after a string of undersea power and internet cables were suspiciously severed, Russia's shadow fleet is getting extra attention.

A Bulgarian ship has been released after Swedish authorities cleared it of deliberately sabotaging an underwater cable in the Baltic Sea. NATO has moved to protect Baltic Sea cables amid concerns of Russian tampering.

After several suspicious submarine cable incidents, NATO launched a naval operation in mid-January to secure its infrastructure. This coincides with the Baltic states' scheduled disconnection from the Russian grid and connection to Europe's grid by February 7.

Northern Europe’s Baltic Sea is bordered by nations including Germany, Russia and Latvia. Many critical cables and pipelines cross the seafloor. But with tensions rising in the region, NATO is looking for ways to ensure all that infrastructure stays safe.

Under steel grey skies, the Dutch minehunting vessel Schiedam cuts through the waters dividing Denmark and Sweden, part of NATO's Baltic Sentry mission to protect underwater infrastructure in the Baltic Sea.