Islas Regulating Reservoir: Main Renovation Work begins in June

12.05.2026 - Albula-Landwasser Kraftwerke AG (ALK) is currently renovating the Islas regulating reservoir, investing approximately 5.3 million Swiss francs in the project. The reason for this is progressive damage to the reservoir’s waterproofing. After ALK carried out various preparatory works in the summer of 2025, the actual rehabilitation work on the regulating reservoir will begin in early June.

In brief:

• The Islas regulating reservoir is part of the Bergün-Filisur power plant stage of Albula-Landwasser Kraftwerke AG (ALK), completed in 1966.
• Regular condition assessments by ALK staff have revealed that the condition of the basin lining has deteriorated.
• To ensure long-term operational safety and prevent energy losses, the basin must undergo comprehensive renovation.

The Islas regulating reservoir has a usable volume of approximately 35,000 cubic meters. This is where both the water from the Albula River and the water already used by the Tischbach power plant are collected and fed into the pressure tunnel to Filisur. Because the condition of the basin lining requires renovation after more than 60 years of operation, ALK has decided to replace a large portion of the lining. ALK is investing approximately 5.3 million Swiss francs in this long-term maintenance project.

Work will take about six months

Renovation work on the Islas equalizing reservoir will begin in June 2026 and is expected to last until fall 2026. During this time, the reservoir will be completely drained. Afterward, the damaged surface layer of the embankment will be milled off and a new asphalt seal applied to the reservoir. At the same time, concrete repair and utility line work will be carried out.

To limit water losses for power generation and to ensure the safety of construction work during the repair phase, various preparatory measures were already implemented in the summer of 2025. These include a new relief structure and a temporary diversion of water from the Tischbach stream to enable the plant to continue operating in bypass mode while the basin is drained.

Albula Landwasserkraftwerke AG is a joint venture between Axpo (75%), EW Davos (15.74%), the Canton of Graubünden (5%), and various municipalities (4.26%). The concession for the operation of the Albula-Landwasser power plants runs until 2046.

Note for editorial offices

• Regulating reservoir: A regulating reservoir is a water storage facility at hydroelectric power plants that temporarily stores water and can release it selectively for electricity generation—this allows electricity production to be flexibly adapted to current demand.