Unteraegeri / Zug, 15.05.2023

Local flooding on Lake Aegeri: Lake Zug level also high

Lake Aegeri has recently overflowed its banks in some places. Nevertheless. the operations manager of the hydroelectric power plants in Neu- and Unterägeri is confident that the situation will ease.

A reader's video showed: Lake Aegeri has been unable to swallow the masses of water that have rained down from the sky in recent days. This is despite the weir, which has been "fully open for days", according to Philippe Wehrli, operations manager of SAE Immobilien AG and responsible for the level of Lake Aegeri.

Link to reader video: https://www.pilatustoday.ch/zentralschweiz/zug/aegerisee-tritt-ueber-die-ufer-151476254

"The current level at noon on Friday was 724.23 metres above sea level," he reports. And illustrates with an example of why the lake has overflowed its banks. "It's like when a host pours a glass too quickly. At some point, what flows in can't flow out again fast enough."

Law of the Sea Treaty regulates the opening of the weir
A maritime law contract regulates when the weir must be opened: this must happen at a water level of 724.00 metres above sea level. Due to the current situation and the weather forecasts, however, Philippe Wehrli already opened all the gates at a level of 723.97 metres above sea level.

This footbridge in Lake Zug only just out of the water       Photo: Daniel Hegglin / Facebook
The level of Lake Zug has also been rising for days              Graph: Federal Office for the Environment
Lake Aegeri has recently overflowed its banks in some places        Reader photo

The water from Lake Aegeri flows away down the Lorze river. In an earlier article in the Zuger Zeitung newspaper, the operations manager explained that he could control up to two centimetres of the level of Lake Aegeri in one day by discharging water into the Lorze river.

Intensive study of weather forecasts
He consults the weather forecasts regularly, but is doing this more intensively at the moment. And he is confident that the level of the lake will drop in the coming days because the weather forecast for the coming days is reasonably dry. If there is more heavy rain, however, the level could remain constantly high.

Philippe Wehrli, who in his capacity as the person responsible for the level of Lake Aegeri is intensively involved with nature and its phenomena, says: "We have to bring nature into balance, then many problems can be solved."

Lake Zug is filling up
Following the many days of heavy rain, Lake Zug is also filling up with more and more water. The water level on Friday morning was 413.93 metres above sea level, which is 7 centimetres below the yellow danger level.

The Zug photographer Daniel Hegglin posted a picture showing a footbridge in the lake that is only just above the water level. He wrote: "Lake Zug is filling up. Water level as high as usually only in summer."