Parts of the Rhine river in Germany could soon become unnavigable as water levels drop further due to soaring summer temperatures and low rainfall, an industry group warned Monday.

Rhine river water levels have been at record lows since the end of July as Germany, like elsewhere in Europe, struggles through a series of heatwaves.

Cargo ships have managed to continue transporting goods along the waterway, which flows through the industrial heartland of Europe's top economy, albeit with reduced loads and at higher costs.

But the BDB association of inland shipping warned the water level at the town of Kaub -- used as a reference point for vessels plying the waterway -- is expected to fall even further this week.

"With water levels this low, commercial shipping will no longer be able to transport goods in the region," the group's managing director Jens Schwanen told the Rheinische Post newspaper.