Unreal Engine 5.1 River "Overflow" bug

its the first time I encouter this bug, I dont know if its is really a bug or me doin something completly wrong but I really dont get it.

This is just the UE Water River with default settings but it is not properly editing the Landscape, it looks like it overflows.

Landscape is directly imported from a GAEA Heightmap so it should be fine.

Also the Landscape and the River + Ocean are in positive z position (I mention this because in the early days of UE Water the system broke if you set it up in negative z position)

Hope someone can help me there would be very nice.