The Staudinger 5 plant has 510 megawatts of capacity. Is it operated by Uniper and situated on the Main, a major Rhine tributary.

Its output may be "irregular" until Sept 7 "due to a limitation of coal volumes on site" caused by the low level of the Rhine, according to the document on EEX's transparency site.

Germany last month agreed to reactivate its coal-fired power plants or extend their lifespans in response to an energy crisis unprecedented in generations that has been triggered by dwindling supplies of Russian gas.

But the shallow river levels following a hot, dry summer mean that barges taking coal feed stock to generation plants can only sail with partial loads. The same problem caused falls in output at power stations and hit profitability at chemicals manufacturing plants in 2018.

A reference Rhine waterline level at Kaub, where vessels need about 1.5 metres of clearance to sail fully loaded, fell to only 61 centimetres (24 inches) on Wednesday.

A heat wave this week has also caused rising transport prices on the river as fewer vessels can pass it and other choke points, tightening transport space.

Low water likewise impacts power prices [EL/DE] as well as other commodities such as mineral oil products and grains.

Warming rivers in recent weeks have also curtailed French cooling water supplies to nuclear plants, contributing to tightness in the European power system and driving up spot electricity prices.

(Reporting by Vera Eckert, editing by John Stonestreet)