I once (either here or on the internet) saw a design from a contraction that was scooping up water and rotating on 'gravity'

and by doing so 'adding oxygen' in the fishpond

Does anyone have a link to that or a similar devise???

thanks

Without running water, you're asking about a perpetual motion machine. Not likely.

I did once see a toy that looked like a birds' head on one end, with a counter weight on the other. A rod a few inches long separated them, with a pivot in the middle. The "bird" would pivot down, dip it's beak in a glass of water, a few seconds later pivot back up. Repeat.

I can only guess at the mechanism, capillary action and evaporation changing the balance maybe, but scaling that up to do any useful work seems a problem.