Yes his stuff is great 
I’m not sure what the best approach will be for sections of river that need to blend to the ocean but it may still be possible to use the water materials from the plugin to do the ocean without any landscape edit layers and with a fixed z-height at world zero.
Either way, for anyone thinking about the water plugin I think the best advice is don’t touch it. It will cause you more headaches than it’s worth and the in-editor performance is not worth the convenience of avoiding doing riverbeds with meshes or landscape sculpting.
Hopefully one day UE will fix it but for now I agree Hochban, it’s just not worth touching this broken mess. It would honestly be better for them to remove it altogether than to keep it in broken since - given the number of tutorials and videos out there directing people to it - it’s going to be a huge time-sink for new developers learning the hard way that it’s better to just avoid it altogether.
The funny thing is too, the materials are good…as is the post-processing. It’s so close to being functional but they missed the mark.
All Epic really needed to do was make river spline meshes that don’t affect the landscape with some more features like vertex painting, mesh distance field effects around static meshes, rapids etc., and maybe some vertex painting for fading so that it can blend into an infinite ocean plane.