Aarau celebrates 500 years of historic stream cleaning festival

Residents of Aarau, Switzerland, commemorated the 500th anniversary of Bachfischet, a tradition rooted in the city’s need to clean and maintain its artificial stream, the Stadtbach.

The annual event began as a necessary civic duty in 1526, when city records first mention it. The Stadtbach provided essential water for drinking, fire control, and local industries, making its upkeep vital for the medieval town’s survival.

Each year, citizens would temporarily dam the stream to clean its bed, a process lasting four days and requiring households to store water. The timing of the cleaning traditionally occurred in September, after the harvest and before the grape harvest, when labor and equipment were readily available. In 1784, a major fire interrupted the cleaning, prompting officials to immediately refill the stream as a fire safety measure. Over time, the Bachfischet nearly disappeared.

By 1922, only a few people still participated, as modern water systems diminished the stream’s importance. The Heinerich Wirri-Zunft, a society founded in 1922 by physician and politician Eugen Bircher, revived the custom. Today, the Zunft continues to preserve the tradition, which now involves children parading through the darkened city with handmade lanterns and a symbolic burning of the lanterns at the event’s conclusion.