The 90-minute "tour de aqua" as the Groupon stated, was actually an hour of waiting around and being transported each way, and about 20 minutes of actually being on the raft.
The tour itself was pretty interesting, getting to see the dam from the river and seeing firsthand how things were transported while building the dam.
It was worth the Groupon price, but I would have been pretty upset if I paid full price for this.