The lazy rivers in the water parks don't have a slope. They work on current flow made by the pump. The river itself is level. This is from my observation of one in Georgia. You would need the current pushed by one huge pump and the waterfall ran by a smaller one. You are talking a lot of money and a high power bill.

Happy ponding,
Scott

Do you think I could find 3 cheap solar pumps, 2 to generate a stream for the 2 bends, and 1 for the waterfall ? I have 320 days of sun in my area...

This sounds like a neat idea! But I don't know if "cheap" factors into that plan. Seems to me you would need a pretty powerful pump to move that kind of water on a level grade. I suppose it depends on how fast you want the current... are you wanting to use this for fun? Or are you just wanting to create the effect that would be planted or something? What are you wanting to do with it? Will it look natural, or like the photo only smaller?

Perhaps you might ask in the Pools and Spas forum?
Pools and Spas

The lazy river at my local theme park moves on a current, generated by jets of water that shoot out the sides every 20 or so feet. It alwasy made me think of a giant spa with the jets angled in the same direction.

Thanks to both. I will make indeed the same question in the Pools and Spas forum, being a bit more precise. I would like it to look more natural, and I need the stream to be peaceful, not so strong.

there are all KINDS of cheap solar pumps. But they are cheap because they are toys.

Did you build the lazy river? I am thinking about it now