Slightly off topic but as we are talking water and the future, eventual, FS4 and possible inclusion of water. I was thinking aloud here so it may not work.
If you built an airfield in the middle of your lake. And
If you had a fully modelled runway and taxi ways at the lakes height. 3DS Max or that other program whose names escapes me, will be needed until the gods deem we are capable of using a blender plugin (rant over). And
If the runway and taxi ways were marked with floating cone's or buoy's. To ensure you stayed on the narrow path. And
If you built a small jetty or similar. And
If you applied the same texture, specular and bump mapping to runway and taxi way. And
If you had a ground plane with the above maps etc, scaled of course. And.
Well that's it really, you should have a fully working water landing strip. Maybe a few tweaks. And a big AND.
If someone developed an aircraft with floats. As 3rd party aircraft development is nil as far as I can see, I wouldn't hold your breath, Scuba gear needed for that.
Just the ramblings of an old man
PS, you could even add little lights on your buoys or cones for night time landings