Not enough coal on site could force the energy company Uniper SE to cut back on electricity production at a hard coal-fired power plant.

In the Staudinger 5 power plant in Großkrotzenburg, Hesse, there could be irregularities in operation by September 7th, the operator said.

The cause is the low water level of the Rhine, which is an important transport route for fuel.

The river's water level is nearing the point where it is practical for transporting large volumes of goods.

The low water levels reduce both the number of ships that can still be used and the amount of cargo that the ships can transport.

Uniper itself expects the restrictions to last until September, leaving just a few weeks before the start of the colder months, when coal will be needed to fill the gap caused by dwindling gas supplies from Russia.

Low river levels in France

Low river levels also affect nuclear power plants in France.

A heatwave is driving up water temperatures and limiting Electricite de France SA's ability to cool some assets.

The French utility said power stations on the Rhone and Garonne rivers are likely to produce less electricity in the coming days, but that there will be a minimum level of capacity to keep the grid stable.

Power plants typically require cooling water, which is typically hauled in from a nearby river or sea before being returned, often at a higher temperature than when it was received.

To protect fish and other aquatic life, the water must not be too warm.