Scientists in St Petersburg, Russia have been using crayfish and snails to monitor pollution levels.
The heart-rate stress of the crayfish and snails are monitored and compared to levels recorded before putting the crustaceans into potentially polluted environments.
The crayfish are put into the river Neva while the snails breathe air from an incinerator which burns St Petersburg's sewage. These creative methods are vital to the protection of the city's four million people.
Al Jazeera's Barnaby Phillips reports from St Petersburg