https://en.wikipedia.org/wiki/California_Aqueduct
I don't think of them as parts of navigable waterways!
Edit: Apparently there are some, mainly on the Erie and Chesapeake and Ohio canals.
https://en.wikipedia.org/wiki/Category:Navigable_aqueducts_i...
https://commons.wikimedia.org/wiki/Category:Canal_aqueducts_...
The Erie Canal is still operating along with some of its aqueducts, while the Chesapeake and Ohio canal has been shut down and it seems most of its aqueducts are no longer maintained or operational.
I don't think I ever knew about that. Maybe it's better-known to people who live in the vicinity of those canals?
Artificial navigable waterways are a lot more pervasive in the Netherlands than here. :-) Maybe partly because the U.S. is a lot hillier.