Both the "under stage" - installations below stage level that are invisible to the audience - and a low-lying building adjacent to the theatre were under water at one point.
Bayreuth was hit by a cloudburst about an hour before the curtain was set to rise on a production of "Siegfried", the third part of Wagner's four-part "Ring" that is currently being staged at the annual Bayreuth Festival.
The downpour was so heavy that a number of guests who had driven up Bayreuth's Green Hill to the Festspielhaus could not make their way from the car park to the theatre itself, festival spokesman Peter Emmerich said.
"It was a veritable torrent. Within the space of just a few minutes, there was about half a metre of water in the corridors," Emmerich said. An orchestra musician told AFP that had the downpour continued and the water continued to rise, the performance would have had to be called off altogether.
"The technical staff and firefighters were pumping like mad. There was a danger that the water would have caused a short-circuit. Ten minutes more and there wouldn't have been any performance," the musician said. In the end, the performance began at 4:00 pm and ended at 10:20 pm, only 10 minutes later than scheduled.