Authorities in both Germany and France have announced a relaxation of environmental rules at a number of nuclear power plants, sparking an outcry from ecologists who say local rivers are at risk.

The southern German states of Bavaria and Baden-Wuerttemberg have ruled that plants can pump warmer water back into rivers than they are normally allowed due to the ongoing heatwave in the region, to avert electricity shortages.

Two plants in Baden-Wuettemberg have lowered production 20 percent due to the high temperature of water used to cool the reactors, and Germany's oldest nuclear plant at Obrigheim was told last week to switch off until the heatwave abated.

Environmentalist groups blasted the decision to ease the rules, saying even a temporary increase in river temperatures could be lethal to wildlife.

"The warmer the water in the rivers, the lower the level of oxygen it can hold, which increases the likelihood of fish dying," said Greenpeace spokeswoman Susanne Ochse.

France, where atomic power produces nearly 80 percent of the country's electricity, has also authorized state-owned utility EDF to expel warmer water from six nuclear plants.

The coalition Sortir du Nucleaire (Out with Nuclear Power) denounced the move as "scandalous dispensations with the sole purpose of protecting nuclear energy," warning of grave consequences for the environment.

Prime Minister Jean-Pierre Raffarin said that "exceptional measures had to be taken" at the power plants and "were taken in a timely fashion," in a statement on the concessions granted to EDF.

While France stands by nuclear power as a relatively clean source of energy, Germany has decided to mothball its 19 plants over the next two decades on the initiative of the ecologist Greens party, junior partner in the ruling coalition.

In Switzerland, one of the country's five nuclear power stations, Beznau, has slowed production by 15 percent due to hot water in its cooling system while three others are offline for routine summer maintenance work.

The country, however, primarily uses hydroelectricity and has reported sufficient water levels at its dams.

The Krsko nuclear power plant, shared by Croatia and Slovenia, has dropped output to only 20 percent to avoid overheating the Sava river, according to press reports. The Sava has dropped to its lowest level in 160 years due to an enduring drought in Croatia.

This year's scorching temperatures have sent energy consumption soaring -- reversing the usual European summertime trend and leading to calls for consumers to cut back on their use.

Electricity consumption in steamy Spain has rocketed by 15 percent since the start of August over the same period last year, with popular tourist destinations such as the Balearic Islands and Andalucia seeing a 21 percent rise in demand on some days.

As a result the grid has at times struggled to cope and on July 21 300,000 residents of the Balearic island of Mallorca suffered a six-hour power cut.

Devastating forest fires in Portugal have also taken their toll on the electricity supply, with 100,000 homes plunged into darkness between mid-July and early August.

Damage to power lines may lead to further outages down the road, said utility Electricidade en Algarve.

Authorities maintaining the Dutch national grid on Sunday issued their first so-called code red for a possible power shortage in almost a decade and were forced to renew the warning Tuesday.

Austria, which has no nuclear power plants, relies on hydroelectric power and has seen water levels drop dramatically in recent weeks.

But the suffocating heat is also melting Alpine glaciers, supplying dams with excess water and compensating for the lower levels at river dams, said a spokesman for OEST, Austria's top electricity producer.

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