In the mid-1990s Mauvoisin Hydropower Ltd. planned to increase the output of the existing plants by 550 MW to a total of 902.5 MW with the new Mauvoisin II hyropower scheme. In terms of construction, This increase in output would have been realized by a new 21 km system consisting of a pressure gallery, a pressure shaft and a surge tank between the existing Mauvoisin reservoir and a new underground power plant in Riddes in the Rhone Valley. No additional water would have been used. Ecological aspects were considered early in the planning and design of the plant considered. In order to avoid adverse effects on the water supply in the Rhone due to the concentrated turbine operation, an compensating basin with a volume of around 0.5 million m3 would was planned in the plains if the Rhone Valley. considered early in the planning and design of the plant considered. In order to avoid adverse effects on the water supply in the Rhone due to the concentrated turbine operation, an compensating basin with a volume of around 0.5 million m3 would was planned in the plains if the Rhone Valley.

Despite the existing agreement with the environmental organizations, existing construction permit and valid offers for the construction work and the electromechanical equipment, the project sponsor ultimately waived the project due to overarching economic considerations.