Are there any restrictions on where you can build waterwheels?

[Urban Ranger]

Other than on a flat tile next to a river? Coz I can't build waterwheels sometimes even after these requirements are met.

[Badtz Maru]

You can't build one if you have another watermill adjacent to that square, across the same river. I don't know how it decides what river to put the wheel next to in squares where more than one side is bordered with a river or if that limitation applies if it's adjacent but against other river - WM||WM is not allowed for sure, I don't know if WM||WM|| would be.

[Urban Ranger]

Yup, that sounds right. Why don't they mention these things? Why is there this additional restriction as well? Argh.