Apparently swimming burns between 500 to 900 calories per hour (depending on which website you look at, level of effort, and your weight; seriously there are a lot of variables here). I've already been given the advice to eat a bit before the morning workout so your body has something to burn but I've also noticed that I am eating a lot more during the day.
I can't be burning *that* many more calories but I guess after years of my highest exercise being getting up from the couch to find the remote, walking to the copier, and riding a vespa, then swimming 30 minutes is a lot.
I just downed a couple of packs of instant oatmeal, hopefully that can hold me off until lunch. Unless I have to walk to the copier a few more times.