u/srb846 is correct -- it's a water wiggler that also glows with a rainbow light at dusk. By keeping the water moving, it keeps mosquitos out of the water and attracts the birds. There's a chickadee that I often see standing under the dome, letting the rotating bumpers swish its tail feathers. I used to worry that the agitator would tangle its feathers, but it flies away without a problem, and returns to repeat the fun.
Yes, exactly!