Barges moving goods from the Rotterdam area to clients in the farthest stretches of the Rhine can only operate at about half normal capacity as water levels drop, according to Interstream Barging.

Vessels bound for Karlsruhe, Germany, and into Switzerland can carry 1,200 to 1,300 tons, the operator said by email. That compares with the usual 2,500 tons. Capacity cuts have been in place for several weeks as water levels along the river — a vital artery for European trade — fall below the seasonal norm.

The Rhine is used to transport millions of tons of oil products and other major commodities across the region. The cost of moving diesel to the Karlsruhe area has been rising since the end of May and is the highest for the time of year in well over a decade.

Vessels traveling to the Upper Rhine need to pass a narrow part of the river, south of Cologne, where water levels are at a multiyear seasonal low. Last year, trade along the waterway was severely disrupted for the same reason, affecting oil refining, power generation and more.