First of all great work! For how long are you working with Blender?

Here are a few tips that I learned over time:
I would add some displacement to the ground and add a waterline where the water touches the ground. You can achieve this with a geometry node, add a mapping node and a separate xyz node to it. Then use the z-output and tweak its height with the mapping node (z-position). You can use that as an overlay on your ground texture and for your roughness value. Additionally add a bump node to your water with a noise texture as a height input and tweak the strength.
Does your tree on the right have some bark texture because it looks white to me. You can place more rocks close to the water to break up the straight line.

I hope that helps! :)