River Left and River Right is all about the direction of travel of the water and its relationship to the banks. As you face downstream with the flow the bank to your left is river left and the bank to your right is river right.
In the image above the kayak is roughly facing downstream. The house on the right is river right.
In the image above the kayak is facing upstream. On the left you can just see the same house that was in the first image. Despite being on the left the house is still river right.
This remains the same which ever way you face, river right is always on the right as you look downstream etc…..
If I was asked/told to “Boof Left”, I would boof towards the river left direction.