Oil slicks, sewage, industrial waste and rubbish floating sea is harming wildlife and could lead to marine crisis.
A favourite for glamorous pictures by Instragram fans yet visitors are warned to take extreme care.
Krasnoyarsk's skies have been black since the start of the New Year, with locals complaining of 'chemical smell', lack of oxygen.
Yet nickel capital Norilsk - the city with the highest industrial emissions - does not feature in the top ten.
The famously clear waters of Baikal - the world's deepest and oldest lake - are under threat from tourists, says leading scientist Maxim Timofeyev.
Shocking pictures reveal colour of Daldykan River with locals claiming the waste from a nickel plant is to blame.
Call to locals and tourists to aid experts counter the green gunge 'polluting' world's deepest lake.
Permafrost remains of long-gone woolly rhinos, mammoths and cave lions bring intriguing scientific breakthrough.
Vet clinics inundated with cases of cats and dogs suffering health problems and rashes in 'Dirty 30' Siberian city.