The Rhine River’s water level at a key waypoint is set to decline in the coming days, curbing the amount of cargo that barges can carry.

The measured level at Kaub, which lies west of Frankfurt, is forecast to fall to as low as 71 centimeters (28 inches) early Monday, according to German government data. At 40 centimeters or below, it becomes uneconomical for many barges to haul cargo through this part of the river.

Snaking roughly 800 miles from Switzerland to the North Sea, the Rhine is used to ship millions of tons of vital commodities through inland Europe, including coal, oil products and iron ore, as well as goods in containers.

The water at Kaub recently fell as low as 30 centimeters, before jumping to 128 centimeters earlier this week. The level is not the actual depth of the river, but rather a measure used to calculate navigability for vessels.

When the Kaub gauge is at -- or above -- 250-260 centimeters, a typical container vessel can sail through the chokepoint fully loaded, according to transport firm Contargo GmbH & Co. KG. But at 75 centimeters, carrying capacity falls to 25%, meaning four ships would be required instead of one to transport the same volume of goods, according to Contargo.