A summer heatwave has lowered water levels for crucial shipping lanes across Europe, driving up costs and stalling cargo moving through the Rhine and Danube rivers.

Reuters reports that temperatures peaked at 95 degrees Fahrenheit in Budapest, Hungary by the start of July, after the region received just 17% of its normal rainfall for the previous month, marking its driest June since 1901. The resulting low water levels mean that cargo ships transiting the Danube River have only been able to operate at 30-40% capacity, prompting ship operators to impose surcharges on cargo owners as high as 100% for vessels that aren't fully loaded.

Recent triple-digit temperatures in Germany have led to similarly low water levels for the Rhine River, where cargo vessels transiting a chokepoint through the town of Kaub have only been able to sail at 50% capacity, and have been traveling at just 40-50% capacity through Duisburg and Cologne. Moderate rain is expected to slightly raise water levels in both Germany and Hungary during the week of July 7, although extreme temperatures are still expected to persist for much of the summer in Western Europe.

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The Danube and Rhine rivers are the first and second longest rivers in Western Europe respectively, and are relied upon to ship a variety of goods, including coal, car parts, grains and chemicals. Issues with low water levels have coincided with an ongoing strike at the Port of Antwerp in Belgium, as well as widespread reports of congestion at several European shipping hubs. A heatwave also led to a series of technical outages at the Port of Rotterdam in the Netherlands on July 1, where operators were forced to temporarily close two terminals to trucks while crews worked to restore systems.