Yep, I found a dearth of underwater maps when I was considering the finale to my campaign arc. I've always shied away from underwater games because the rules looked so complicated. However at high levels with lots of freedom of movement spells and enchantments like cloak of the sea, the play is actually identical to a high level encounter anywhere else as swimming underwater becomes identical to flying. Now it makes targeted dispel magic (or worse - anti-magic rays) much more dangerous, but that's a fun twist for your players to find out about.
I love high level play and I hope that this provides a useful environment for some people here to use for their players.
I'm actually using this in early paragon tier myself, because sometimes you just need to do something that's a bit different and interesting. Plus it gives me lots of creepy possibilities rules wise!