There is nothing wrong with the appearance of Italy's magnificent lakes.

The water of Lago di Como -- Lake Como -- surrounded by strikingly high peaks, is deep blue and as clear as if it has just come tumbling out of the Alps.

The hamlet of Laglio, on the west shore of the southwesterly fork of Italy's third-largest lake, has been enjoying a boom since the actor George Clooney bought not one but two villas there.

Visitors crowd the little beach, too, families squashed onto towels enjoying the heat wave, children gambolling in and out of the water. There is a sign that says "No Bathing" but no one pays any attention. What possible harm could lurk in this sparkling water that's more than 400 metres deep, with the bottom of the lake more than 200 metres below sea level?

Well, plenty, according to Legambiente, Italy's most prominent environmental organization.

The "No Bathing" sign is there for an excellent reason.

Clooney has found a great house with a marvellous view, but the water is sick. And not just slightly under the weather. The latest snapshot of pollution in Italy's lakes indicates that Laglio has one of the worst-polluted lake beaches in the country.

Bacteria is measured in terms of "colony-forming units" or cfu, a measure of viable bacterial numbers per 100 millilitres of water. The upper permitted limit of cfu for lake water that is safe to bathe in is 100. But at Laglio the figure is 6,800 -- 68 times too high.

The shocking figures, repeated right across the Italian Lakes region and in two of the biggest lakes in Umbria, emerge from a second year of spot checks by the Legambiente agency.

"We started to monitor the lakes last year," said Stefano Ciafani, scientific director of the organization, "and we found a level of pollution equal to that of 20 years ago.

"Italy's salt water is clearly better than it was, but not the lake water. On Lake Como this year we have found a worrying situation from the point of view of microbiological pollution," he said.

"The problem of purification has not been resolved, and this applies to all the municipalities that border the lake, and also those at some distance from it, which use the rivers that discharge into the lake as sewage pipes."

George Clooney fans and others who succumb to the temptation to cool off in Como's azure waters are taking a serious risk. Skin infections and dermatitis are among the routine hazards, while on the worst stretches, such as that which laps the shingle outside Clooney's Villa Margherita, the biologists in Legambiente's travelling laboratory warn that there is the possibility of contracting something far nastier, such as salmonella.

Damiano di Simine, president of Legambiente's Lombardy region, told La Repubblica newspaper, "The pollution is caused principally by the inadequacy of the purifying systems built in the '70s and '80s, that are too small and don't work properly."

The organization doesn't claim that its findings are exhaustive, but they are up to date: the travelling lab took 150 samples from 22 lakes in June and July.

Few of the lakes tested emerged well from the exercise.

Lake Garda is one that has improved. Last year there was a blue-green algae emergency in the lake, but this year it is relatively healthy with 42 per cent of samples within the norms.

But of those tested, only Lake Caldonazzo in Trentino was found to be in optimal condition.

The sickness of the lakes is the result of many factors: evermore intensive agriculture that produces toxic runoffs, illegal housing and industrial developments that discharge effluent into the lakes, global warming which means there is less rainfall to replenish them. And demand for their waters continues to soar.

"It is still possible to save our lakes," said di Simine, "but the Lombardy region says it is in financial difficulties as it is. In 2000, the EU's Directive 60 laid down that all Europe's lakes should provide good quality water by 2016. But Lombardy has already said it is unable to meet the required standard for Lakes Idro and Lugano", two of the worst offenders.

"But we are among the richest regions in the country. If we can't find the money, who can?"