Outdoor theatre - How did the dead falls die?

Sweden is not an obvious choice for outdoor theatre. Even in summer the weather is not dependable and both the actors and the audience are out in the weather. However, since the time of the Vikings weather is not seen as a problem and Ruth proposed a visit to Dödafjallet, the Dead Fall, where we could see a play about how the falls came to be dead. It was a joint birthday present for Jan and I, and it turned out to be a very successful evening, so thanks very much Ruth, for the idea, the transport, the tickets, and picnic you provided!
The rain just held off, the breeze kept the mosquitoes away and everyone in the audience had enough jumpers, jackets, blankets etc to stay warm. The play itself is fun and interesting and the countryside and views are fantastic, as I hope you can see in the image here.
This is one of five "stage" areas around a circle, one of which actually is a stage. The audience sit in the center of this circle and the whole seating area revolves between the various sets.
Today you can visit the Dead Falls and walk where the river once plunged 35 meters down from a lake that no longer exists. It really is spectacular and I can recommend both the play and the place to anyone travelling by.
So how did the falls come to die?
There isn't room for a detailed explanation here but it involves an engineering project that went spectacularly wrong in 1796, showing that optimistic engineering and environmental catastrophes are nothing new! Read more on Wikipedia!