Strait of Hormuz tanker backlog grows as barnacles slow post-ceasefire reopening

The Strait of Hormuz is facing a new shipping problem after the ceasefire that ended the Iran-Israel-US war was expected to restore traffic quickly. Instead, hundreds of tankers remain anchored in the Persian Gulf and the Gulf of Oman, leaving one of the world's most important oil chokepoints only partly reopened. The immediate obstacle is no longer only security, but also marine growth on ships that have been idle for months.

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According to Saudi Aramco chief executive Amin Nasser, more than 600 tankers were stuck inside the Persian Gulf as of mid-May 2026, with another 240 waiting outside the strait. The International Maritime Organization had earlier estimated that around 20,000 mariners and 2,000 ships of all kinds were stranded in the Gulf, including bulk carriers, cargo vessels, liquefied petroleum gas ships and some military vessels. The report says the long wait has allowed barnacles and other marine organisms to build up on hulls, creating a practical delay to restarting normal operations.

The problem matters because biofouling can make ships slower and less efficient, and in severe cases can increase hydrodynamic drag by 10% to 60%. The article says vessels anchored for three months or more are especially vulnerable, and that cleaning the growth is left to divers known in the industry as bottom cleaners. In the shallow, warm waters of the Persian Gulf, conditions are favourable for barnacles, mussels, clams, tube worms and algae, which attach quickly to stationary surfaces.

The Strait of Hormuz is a critical route for global energy trade, and any disruption there can affect oil flows well beyond the region. The supplied report links the current backlog directly to the months of conflict and the shutdown of sailing through the strait, which left ships waiting in place for an extended period. That makes the reopening more complicated than a simple return to normal navigation, because the vessels themselves now need maintenance before they can move at full speed.

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The wider context is that the Gulf's warm, shallow waters are unusually suited to marine growth, and the longer a ship remains still, the more likely it is to need cleaning before resuming service. The report also notes that the strait's reopening had been expected almost overnight after the ceasefire, but the scale of the backlog has changed that timeline. Saudi Aramco and the International Maritime Organization are among the key actors referenced in the developing situation, alongside the shipping industry and crews now dealing with the consequences of the stoppage.

What remains unclear is how quickly the anchored fleet can be cleared and how much delay biofouling will add to the return of normal traffic. The report does not give a timetable for full recovery, and it is not clear how many ships will need cleaning before departure. The next developments to watch are whether traffic through the strait increases, how quickly bottom-cleaning crews can work, and whether the backlog begins to ease in the coming days.

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