I want this. I need this. I have no idea where I would put this, but man, you can you imagine playing Pirates on a gaming table like this? It was built by Gale Force Nine for WizKids to run Pirates games at the big conventions. I can't wait to see it at GenCon this year!
I'm guessing its an epoxy resin, as described in this ModelRailroader.com article: Make a realistic lake for your model railroad. The mountain lake in the article has the same sort of sheen as the Gale Force 9 model; use brighter blues and you'd get coloration similar to that in the GF9 photos.
Try blue jello for water! If your ships and squids are clean enough, you could eat the sea after you battle on it. Almost as cool as playing chess with those shortbread chessmen, and then eating your opponent's pieces as you remove them during the course of the game.
If I played games with miniatures on any sort of a regular basis, this is what I'd do:
First, take a regular folding table. Any size, just something that can be folded up and tucked away.
Attach a thin sheet of steel to it. Readily available at any home center, most of whom will also cut to size. Make sure the steel is slightly smaller than the table so it doesn't stick over and leave dangerous sharp edged.
Upholster the thing with some sturdy but relatively thin fabric. Possibly edge it with elastic so it can go on and come off like a fitted sheet, in case it needs to be washed. Maybe make several in colors -- green for sure, maybe blue.
Build terrain pieces, and attach magnets to the bottoms (you saw this coming, right?). The pieces can then be arranged as desired. Use the green slipcover for forest and field, the blue one for water, etc.
When you're done the pieces can be boxed up and the table can be hidden away.
If you want to use regular battlemaps or incoroprate them, you can hold the corners down with magnets. You can even put magnets on minis, so they don't fall over or get trampled by housecats, etc.