Alright, to try to help further here, can you either upload the file you’re having trouble with, or (if this file is for a project where you’d rather not have that file floating around on the Internet), upload a file where you replicate the issue with a different terrain? I can’t seem to replicate the issue on my end just going off of what you’re saying, so I’m starting to think there may be a different underlying problem here.
Edit: After spending a bit more time trying to replicate your issue, here’s a couple parameters you could try adjusting to smooth out those rivers.
In Flow Restructure, try adjusting the Ridge Carving parameter. By default it’s set to the highest value, I’ve found by lowering it, you can get smoother results from a Create Water node following it.
In Create Water, try adjusting Minimum Water Depth and Discharge Scalar. It’ll take a lot of iterating, but I’ve successfully used those parameters to smooth out harsh river channels in a test scene.
If any of these parameters seem to have an effect, it may just take a balance of all three parameters to smooth them out in a way that you like. The Flow Speed parameter in Create Water may have an effect as well, but I didn’t notice any changes when playing with that parameter alone. Failing all of these, an upload of a tmd where the problem you are facing is present would still be very helpful in further trying to troubleshoot this.