A River, a City, and Eight Unexpected Guards
In Poznań, Poland, the safety of drinking water rests in the shells of eight mussels. Housed inside the Dębiec Water Treatment Plant, they are wired with tiny sensors and given remarkable responsibility: if the water becomes unsafe, they shut down the city’s supply.
How Mussels Took Charge
The Warta River, Poznań’s main water source, flows through old industrial regions where pollution has long been a concern. Heavy metals like chromium posed particular risks. In 1994, engineers turned to bioindicators to ensure safety. Mussels, sensitive to toxins and quick to react, were chosen.
When the water is clean, they open fully to feed. When pollution rises, they clamp shut, triggering alarms. If four of the eight mussels close simultaneously, the system automatically cuts the supply.
Tested, Proven, and Still Working
The method was developed at Adam Mickiewicz University’s Department of Water Protection and found reliable. Each mussel has a spring sensor glued to its shell, connected to computers that monitor behavior alongside artificial chemical sensors.
The system accounts for natural quirks—an individual mussel may close to rest—but the collective reaction is what matters. Though mussels are often seen as pests clogging pipes, here they became indispensable partners in water safety.
Beyond Poznań: Fat Kathy in Warsaw
The idea spread. In Warsaw, the Gruba Kaśka (“Fat Kathy”) pumping station in the Vistula River also relies on eight clams to monitor the capital’s supply. Director Julia Pełka, who grew up crossing the bridge above the station, later made a documentary about them.
She worked with malacologist Piotr Domek and Polish Waterworks to capture the unusual guardians at work. In both cities, clams are replaced after three months and released into safe waters, as they gradually lose sensitivity to contaminants.
A Lasting Partnership
The clam-powered system has safeguarded Poznań’s water since 1994 and continues to operate today. The Warsaw system follows the same principle: humans depending on the natural sensitivity of shellfish to detect dangers that machines alone cannot. It remains one of the most unusual collaborations between biology and engineering in modern water management.
In Poznań, eight mussels guard a city’s tap water.
Inside the round Dębiec plant on the Warta River, each shell carries a sensor.
When the river turns risky, the mussels snap shut.
If four close at once, the computers cut the water…🧵👇 pic.twitter.com/V1bX9BfAGW
— Fascinating True Stories (@FascinatingTrue) September 26, 2025