I'm not positive of the river I saw on the show I was watching (It was Planet Earth's "Freshwater" Episode, and they did a mountain river), however it had extremely fast moving water, and one of the inhabitants was a Bamboo Shrimp, the filter feeder ones. I believe another was a Centipede-looking thing, another kind of invert. I'd be interested in learning how something like that could be re-created. I don't think I'd try it, but I think it'd be fun to learn about how I would if I was going to.