Rhino Water Volumn got weird reflection

I got this water volumn, the side of the water volumns got some weird colour block.

I though it will be the normal of the surface, but my side surface is in one single surface, I can not even explore it to flip the normal.

I try create a simple volumn, just a box, it got not problem at all.

So is it because my surface casuing this problem.

Enscape does not have a solution for vertical/volumetric water. It has been a item that has been asked since 2018 but nothing has been done to provide a solution. There are a few forums on here that have certain work arounds that might work for you. Demian will ask you to add your vote to their portal, who knows when it will be tackled.