First, disguise the edges of the pool with some flat stones...slate would work as well as some bush rock...(of course have a log/stone ramp for turtles to get in and out)
Next you need to hide some of that wall, it draws your attention more than the enclosure. I would put some large stones around to break it up a bit and also plant some grass type plants along the edge...(they will get some height to break up the wall but won't allow the animals to climb too high)
Next is to remove the sticks and box in the middle...I presume the sticks are for some sort of climbing/basking species like EWD or Beardies? Anyway, a nice large log on an angle upwards will work brilliantly and you can lay some hides around the base of it...