Known as ‘Gruba Kaśka’--which translates as Fat Kate--the station stands in the middle of the River Vistula, and has, over its many years of service, become a symbol of the city.

Conceived by engineers Włodzimierz Skoraczewski and Stanisław Wojnarowicz, Gruba Kaśka took 12 years to build before it finally started pumping water on September 22, 1964.

Although planted in the middle of the Vistula the station draws water from underground rather than sucking it up directly from the river.

The well is now a fully automated facility, with no human staff working there on a daily basis. But it does, however, boast a permanent staff of mussels that have the vital task of monitoring water quality.

"Their 'shift' lasts three months, after which they return to their natural habitat—a lake. They are replaced by another group of eight mussels ready to take over, and so the cycle continues," one water utility worker told TVP 3, a public television channel.

The system is simple. When the crustation detects pollutants in the water they close their shells. At that moment, sensors attached to their bodies trigger an alarm.