Italian officials are warning of a possible state of emergency amid worsening water shortages and soaring summer temperatures.
Parts of northern Italy are parched
Regional governors in the drought-stricken north have already asked for state help.
Other parts of southern Europe are also sweltering in high summer temperatures.
If there is no rain within two weeks, drastic steps may follow, including limiting water supplies to either agriculture or industry, Italian officials say.
The River Po is at record lows - nearly eight metres (24 feet) below its normal level.
Worst-hit regions include Piedmont, Emilia-Romagna, Lombardy and Venice.
In Venice, rainfall in the first six months of the year was 40% lower than average.
"Water supplies are guaranteed until the end of the month. But if it doesn't rain we'll have to decide what our priorities are - agriculture or industry," said Italy's civil protection head, Guido Bertolaso.
Prayers for rain
There is also a risk that heavy power usage - for example for air conditioning - could create a black-out across north-eastern Italy, La Stampa newspaper quoted him as saying.
One northern Italian power station, at Ostiglia, has already been forced to shut down due to a lack of water to cool its turbines.
The Porto Tolle plant, about 60 kilometres (40 miles) south of Venice is also thought to be at high risk of closure.
Farmers' fields have turned to dustbowls
Up to 2.5 million people could be affected if it is shut down, Italy's
Ansa news agency said.
The water shortage has been worsened by record temperatures in June, which pushed up water usage.
One Italian bishop, in Rovigo, urged his congregation to pray for rain.
There are fears that this year's grape harvest could be hit, along with other crops.