I get that it looks risky, but I don't really see a problem here. The platform is in undisturbed water, no waves, no sudden changes. If the platform is strong enough, which it seems to be to me, it will not easily tip over.
I've worked on a few lifts like that, and if you manage to tip one over I can only say that you were either really stupid or you were trying to do it. All the weight is at the bottom. They are very stable.
The only way to make them fall over is if your floor is not level while driving. Driving is out of the question in this picture, and as long as both guys stay in the fork lift the center of gravity will not change much.
So the platform will not move, the lift will not move, basically they are fine.
If something was to happen you're fucked though.
And different solutions are available. I've personally been in a different lift that had an arm so the lift would be a the side of the pool and the part where I was standing was elevated above the water. That probably would be a better solution, if you have enough space to get one of those lifts in.