Thanks for the info, its quite possible it occurred from the undo bug. I've already disabled flowing water on our server, but we've got a big mess to clean up as its stretching from the cold biome south around the side of our starter island and all the way to the warm biome.
It would be super helpful if there were some way to delete all water above level 90 in the world, though I'm sure that might crash or bog down the server for quite a while when its processing removing all of that water. Also curious how that might affect spawning of future world gen changes like the underwater biomes since now all the areas covered by extra water would be considered modified chunks.