A shadow fleet oil tanker transporting Russian crude had an engine failure as it was passing through Turkey’s Dardanelles shipping strait, forcing a temporary blockage to maritime traffic.

The incident, involving the Hera 1, happened near an entry point to the strait in northwest Turkey at 6:55 a.m., forcing southbound traffic to be suspended for three hours while a salvage operation took place, according to local shipping agents. 

Southbound traffic reopened at 10 a.m. local time and the tanker has now been taken to anchorage. It is a reminder, though, that millions of barrels of Russian petroleum are being moved around the world — often through narrow maritime choke points — without clarity about how they’re insured.

The vessel was heading toward the Suez Canal with a cargo of about 730,000 barrels of Russian crude loaded at the Black Sea port of Novorossiysk, vessel tracking data compiled by Bloomberg show. Its ultimate destination is India, according to shipping information seen by Bloomberg.

Its insurer and beneficial owner are not identified in a database maintained for the International Maritime Organization, meeting a common definition of a shadow fleet vessel.