The water levels in a crucial waterway in Europe’s economic heartland are running dangerously low in the region's searing heat, posing another risk to global supply chains.

The Rhine river — a key shipping lane for coal, car parts, food and thousands of other goods — is experiencing a dry year, CNBC reported. Low water levels mean that river barges will have to travel with reduced freight or even cease operating altogether.

As a result, freight rates will rise.

Millions of tons of commodities are shipped up and down the Rhine, which flows for roughly 800 miles (1,300 kilometers) from Switzerland to the North Sea.  

Read more: Germany Is Re-Engineering Europe’s Most Important River

The water level at the river’s key Kaub bottleneck was at 77 centimeters last week — the lowest seasonally since 2007, Bloomberg reported. If it drops another 37 centimeters or more, it becomes uneconomical for barges carrying commodities to sail past this point.