Egor Chastukhin, an 18-year-old environmental activist, holds a flask to a drain spurting out warm, putrid water near the historic city of Penza in western Russia.

"It smells like herbal tea," he jokes after taking a waft of the sample while Sonia, his wife, jots down notes.

She records the odor and its yellowish color as two other teenage activists, Alexei Zetkin and Yakov Demidov, look on.