[Question] Do I have any reason to worry about a 100m wr watch in the water?

I wouldn't do anything more than splash around in water and light swimming with it if it's only rated to WR 100m. For skin diving or or surface sports I would go with something rated WR 200m or more, like this MDV106. Since your Citizen doesn't have a bezel or push buttons, just remember not to operate the crown when the watch is wet and you should be fine. Also, rinse the watch at the end of the day to get rid of the salt water and prevent corrosion.

Regarding the Skyhawk, again, it's a non-diver rated for 200m with a non-screw-down crown, so I would be wary. However, if you don't operate any of the complications while underwater, it should be fine for general use in and around water.

Here's a table from Wikipedia with some very general guidelines regarding water resistance. If you intend to go scuba diving, I wouldn't wear anything less than a Diver's 200m rated watch adhering to ISO 6425 for complete ease of mind.

/r/Watches Thread