The Rhine River’s water levels risk dropping to an unprecedented low as heat waves grip Europe, creating a bottleneck for the delivery of coal and fuels inland while raising shipping costs.

Water levels at Kaub, a key chokepoint for shipments heading to southern Germany and Switzerland, have already fallen to 28 centimeters, the lowest since 2018, according to German federal data. Forecasts show the barge clearance level could decline even more this week, potentially reaching 24 centimeters on July 31, which would be the lowest in data going back to 1990.

The river, which snakes roughly 800 miles from Switzerland to the North Sea, carries resources including coal, oil products and iron ore, plus goods in containers. As well as impacting water networks, the heat and dryness that have hit the continent this year have stressed power systems, strained public health services and caused major wildfires.

The falling levels on the Rhine are already disrupting freight. The cost to ship diesel from Rotterdam to Karlsruhe — further inland from the closely watched Kaub chokepoint — has climbed to the highest since Bloomberg began compiling the data in 2009. 

The situation is unlikely to improve soon with Europe facing another heat wave. Temperatures in Frankfurt are forecast to reach as high as 39C (102F) on July 30, according to Atmospheric G2, while little rainfall is expected in the coming days.

“With every centimeter it’s getting more difficult,” said Florian Krekel at Germany’s WSV, which manages the country’s waterways. “There’s no rain in sight.”

The disruption is also showing up in coal logistics and supplies. Inventories of the fuel at ports in the Amsterdam-Rotterdam-Antwerp hub have risen about 75% since the spring, according to DBX Commodities Ltd., while barge loadings to move those supplies inland have been cut by three-quarters.

“The Rhine has effectively locked the door on inland coal delivery, and Rotterdam is where the trucks are queuing up,” DBX Commodities chief executive officer Alexandre Claude said.