OpenGL currently does not support FoF compatibility with horizon rendering, it is why a lot of maps designed with OpenGL in mind use a regular floor for water that needs to extend infinitely or instead use a type of border that was more common in old versions of the game.
OpenGL in general still supports just a subset of SRB2's rendering features fully. There are reports of a new hardware renderer being worked on, but the landing date is unknown at this point.