The Rhine River, one of Europe's most important rivers used to transport goods including chemicals, grain and coal across the continent, is drying up because of a record summer heat wave.

Germany's Federal Institute of Hydrology has warned that rivers in Central Europe are at "unusually low" levels that continue to fall.

Most of the 800-mile-long Rhine runs through Germany, Europe's largest economy, but the river also flows through Austria, Switzerland and the Netherlands, as well as along the border between France and Germany.

According to the German Federal Waterways and Shipping Administration, the water level in the Kaub, the river's bottleneck, was 71 centimeters on Tuesday morning. When it reached 77 centimeters last week, it was already the lowest level for this time of year since at least 2007, Bloomberg reported, citing government data.

SWR said the low water level is restricting shipping on the Rhine south of Duisburg and Cologne and that cargo ships cannot sail fully loaded for days.

A spokesman for Germany's Federal Institute of Hydrology told Bloomberg that if the water level in the Kaub drops to 40 centimeters, it will be unprofitable for ships carrying goods to sail through it, given how little cargo they can carry.

Low water levels are already affecting power supplies. According to the EEX exchange, coal deliveries to two power plants in Germany - one in Mannheim and the other in Karlsruhe - have been affected by low water levels in the Rhine since July 13.