How do you create a river for a 3D environment?

I am trying to find an asset that can make rivers and streams.
And just so you guys have an accurate idea of what I mean see the image below:


The blue are the rocky river/stream and the orange are the waterfalls leading to bigger rivers or lakes.
Simply dropping the height to sea level to illustrate lakes, rivers and streams is absolutely not an option.
Doing so would create canyon and not river on my environment.

The best thing I could find are Rivermill Studio and their assets but its not exactly what I am looking for and when it is its a question of quality of the rivers.

 

One solution is to choose a spline-based mesh deform asset. Basically you would create a mesh representing the surface of the river and use the tool to make it conform to the shape of the land it covers. Better yet a generic asset doesn't restrict you to just rivers. Mesh-based roads and pathways, ropes and vines, etc can be handled this way too.

https://assetstore.unity.com/packages/tools/modeling/mesh-deformer-41155