Vital for making its waters so 'pure', one theory is that rising underwater methane leaks are killing off the sponge, but is there a silver lining?
In beach resort of Listvyanka alone, 98 contaminated streams are disgorging sewage and chemical waste into the pristine waters of the world's oldest lake.
Scientist warns of 'environmental disaster' due to 'irreversible' pollution in world's deepest and oldest lake.
Is increased tourism, or a normal natural cycle, to blame for the rapid growth of spirogyra to 50% of the coastline?