The uncontrolled discharge of toxic waste by industry and agriculture as well as dwindling rainfall are transforming many of the country’s rivers into festering pollution hot spots, according to scientists in northern Greece who are planning to grade the dirtiest bodies of water with «black flags.» Using a similar system as the one that tags with «blue flags» the cleanest beaches in Europe, experts from Thessaloniki’s Aristotle University, Ioannina University and the Democritus University of Thrace intend to pinpoint the filthiest rivers in Greece. According to research by these experts, top offenders include the Loudias River and the so-called Trench 66 – an irrigation canal – in the region of Macedonia, the two cross-border rivers Evros and Axios, the Pineios in Thessaly and the Asopos in central Greece. The high levels of copper and chromium in the waters of the Loudias and Trench 66 are believed to have provoked abnormalities in the livers of resident frogs. Local authorities complain about a high incidence of cancer sufferers in their areas, though there have been no tests to determine whether this is true and whether local water is to blame. The Evros and Axios rivers both show high traces of phosphates, nitrates and other chemicals believed to be runoffs from agricultural and industrial activity. The Pineios River is similarly infected. «All Thessaly’s pollution is concentrated here,» said Triantafyllos Albanis of the University of Ioannina. Tests on the Asopos River indicate high levels of chemicals, including depleted chromium, which can cause cancer. The fact that the drinking water of tens of thousands of local residents has been drawn from the Asopos for more than 20 years has fueled public protests.