The river started turning purple 10 years ago, but the people in the small Greek town of Oinofyta who were losing loved ones to cancer never thought of blaming the water.

Factories have been dumping waste in the Asopos River for decades, and nearby tourist beaches were declared unfit for swimming, but there were no official warnings to the people of the town, in an industrial zone about 60kilometres north of Athens.

It took until this year for official tests to show drinking water was contaminated with high levels of a carcinogen, chromium 6. The revelation spread shock and anger in Oinofyta, and beyond, even to US advocate Erin Brockovich - the single mother whose crusade against chromium 6 contamination of groundwater in Hinkley, California, was portrayed by Julia Roberts in the hit film Erin Brockovich.

Used as an anti-corrosive in the production of stainless steel, paint, ink, plastics and dyes, chromium 6 is on the European Union's list of restricted substances and listed as a carcinogen by the World Health Organisation. It poses health risks if inhaled or orally ingested or comes into contact with skin.

Since 1989, the proportion of deaths in the town caused by cancer has risen to 32per cent from 6per cent previously, Oinofyta's priest, Father Yannis says.

"When I heard it was so dangerous that you're not even supposed to come into contact with it I was terrified," says Dina Fouki, a 35-year-old mother of two who has lost her father and in-laws to cancer in the past five years. She and her neighbours will no longer brush their teeth with tap-water. "I have lost loved ones and will lose more. Something must be done," she says.

It is a sorry demise for the Asopos River, which was the scene of one of the great battles of ancient history.

In 479BC a Greek army led by the Spartan king Pausanias crushed the forces of the Persian emperor Xerxes at the Battle of Plataea, saving the Greeks from the hegemony of the east.

Ironically it was the fouling of a nearby spring by the Persians that played a crucial role in the battle.

In Greek mythology the Asopos River was also a god who revolted against Zeus and wanted to fight him. Zeus struck him with his thunderbolt and confined him to bed. Today a putrid stench rises from the river, the waters of which run from red to purple and black and ripple with bubbling sludge.

Despite the obvious pollution, locals say officials have not warned them of the risks in the 30 years since the factories were established.

"When we lost our relatives we started getting suspicious," Fouki says. "But we didn't know. How could we?"

Yannis and biochemical engineer Thanasis Panteloglou forced authorities to take action. After years of campaigning, tests by the state laboratory showed the water supply, contaminated by the Asopos, has high levels of the chemical, also known as hexavalent chromium.