Sometimes the tiny unannounced changes are the most fun. City of Heroes Issue 12: The Midnight Hour, currently in Open Beta, has sneaked a little extra feature in under the radar.
Ordinarily, characters in CoX who fall into the water simply splash about on the surface. You can swim around there, but diving has been impossible, with the tantalizing exception of one narrow shaft in Grandville. This had been the only place where characters could submerge completely, although there was no underwater swimming, just a very surprised Coralax on a coffee break.