I don't believe BP see fish as prey, but to me, it seems unnecessary...they dirty up the water, and the water wouldn't be safe for the BP to consume. Plus the food you put into the water, would likely add chemicals not safe for a BP. I don't know that last part for sure, but to me, it seems like a bad idea.
What kind of waterfall is it? I've heard of snakes and Bp's trying to get inside the waterfall and get stuck.