So this map represents a large ruinous chamber - where the floor has given way, and water has seeped in to flood the cavernous area beneath it (which may, or may not have other 'underwater' exits that lead off to other areas).
And as far as any environmental encounters/hazards go - I thought it might be a nice idea to have the statues on the left hand side show signs that they might have once been highly decorated (jewels might have been set into their eye sockets, or upon the hilts of their weapons, or circling their helms, etc.) - though they have been plundered of their riches long ago.
However, before the room's ruin, there would have been two similar statues upon the opposite wall ...and a character with keen eyesight (and a relevant skill test) might notice the remnants of those statues beneath the waterline (and maybe catch the slight glimmer of something shiny amidst those ruins).
But would it be safe to dive in and investigate?
I also thought that the old wooden planks (that span a few of the gaps) might have a 25% chance of breaking whenever a large, or heavily laden character attempts to traverse them (or a 50% chance if two characters attempt to cross at the same time, or engage in combat, or similar).
But that's just a few things that sprung to mind while drawing the map ...and the main encounter is, of course, left to your own imagination :)