While Fantasmic! was under construction at the front of the Island, the rest of the Rivers of America got a gunite base to reduce water loss. This also reduced the amount of mud in the river, and allowed for show elements to be installed along the river bottom.
In front of the island stage, you can see two of the pits that will house the fountain platforms. During the day, each of the three platforms are lowered into these pits to allow for river traffic to pass above.
A fountain pit at left, in front of the projection room. The small, house-like structure on the right will be home to a bank of speakers.