The saying “you can’t cross over a duck’s river” is a play on words, suggesting that it’s difficult to cross a river that is already filled with ducks. It’s not a literal statement about rivers and ducks, but rather an idiom or idiom-like phrase used to express the idea that something is difficult or impossible to achieve due to the presence of obstacles or challenges.

I used the word “origin” instead of “meaning”, which didn’t seem to work.