Mattmark dam is a reservoir in the Saas Valley of the Canton of Valais, Switzerland.

The lake lies at a height of 2,197 metres above sea level, between the massifs of the Rimpfischhorn and Stellihorn.

[1] The risk involved in constructing the accommodation barracks directly below the glacier tongue, which eventually broke off, was not taken into account.

Seven years after the accident, the Valais judiciary acquitted all 17 defendants, including engineers and managers of Elektrowatt and officials of the Swiss Accident Insurance Fund.

In 2005, journalist Kurt Marti revealed that those responsible for the construction site knew about the dangers of the Allalin glacier and that the court ignored all incriminating facts in its decision.