BDB managing director Jens Schwanen told the Rheinische Post newspaper water levels at Germany's Kaub gauging station, a major bottleneck for Rhine navigation, were forecast to drop into single digits for the first time due to lack of rainfall.
Kaub lies south of the city of Koblenz at one of the shallowest sections on the Middle Rhine.
"Commercial shipping will no longer be able to transport goods in the region at such low water levels," he said.
"The same goes for day trips and cruise shipping.
"In principle, the Rhine is then no longer navigable along its entire length and thus split in two," he added.
Schwanen said shipping would continue between the ports of Amsterdam, Rotterdam and Antwerp, the northern part of the German Rhine and the west German canal network, and farther south there would be traffic on tributaries including the Main, Moselle and Neckar rivers and the Main-Danube Canal.
Germany's most populous state, North Rhine-Westphalia, as well as Lower Saxony, Rhineland-Palatinate and Saarland has relaxed trucking curbs to ease transport bottlenecks caused by low water levels on rivers including the Rhine.
In German cities, including Cologne and Dusseldorf, people can now walk across parts of the Rhine where strong currents normally flow.
The water crisis is being intensified by global warming driven by the burning of coal, oil and gas. Low water levels are also taking a growing toll on ecosystems - and could eventually drive up the cost of clean drinking water.
