Italian prosecutors have begun a judicial inquiry into who was responsible for the dumping of raw sewage into one of Italy's most beautiful resorts, Adnkronos International (AKI) reported on Wednesday.

Two employees from a waste disposal firm in the southern Campania region are alleged to have dumped untreated sewage into renowned Blue Grotto on the island of Capri, under cover of darkness. The two men are currently under house arrest and are due to appear in court next Tuesday, local media reported.

World famous for its clear, shimmering blue water, the sea cave of Blue Grotto is one of southern Italy's most celebrated tourist sites.

The two men were named in news reports as Salvatore Guerriero and Salvatore Criscuolo, from the coastal town of Castellamare di Stabia, south of Naples.

Local police arrested Guerriero and Criscuolo as they dumped 5,000 liters of raw sewage from a tank truck into Blue Grotto via a long rubber tube. The tank truck owners charge 1,600 euros to transport the sewage from Capri hotels, apartments and houses' septic tanks to local sewage plants.

But the workers allegedly dumped the waste into the Blue Grottoto avoid the charges.

"This is an extremely serious incident that shows a grave lack of respect for a great natural beauty spot," Michele Buonomo, president of the local branch of Italy's largest environmental group Legambiente, was quoted by AKI as saying.

"It indicates a sickness that especially afflicts southern Italy -- a lack of mains sewage," Buonomo said.

Almost one-third of the Italian population -- 18 million people-- are not connected to mains sewage and the problem is particularly acute in southern Italy, he said.

Much of the Campania coast is polluted, especially the area around Naples, and Caserta, but also the Amalfi Coast, Buonomo added.

Buonomo believed the men illegally dumped the sewage in Capri's Blue Grotto on the orders of the waste disposal firm to save money.