If you have an android phone, you have to open the app on it, go to your Account (upper right corner where you see the blue square with lines), scroll down to and click on "Advanced Settings", scroll down to and click on "Swim Settings". Fill in the pool length (most exercise facilities like the Y have the standard 25-yard length, some parks have 35-50 yards but will show metric equivalents, most schools and similar facilities have the standard regulation competition 50-meter length). Make sure you know what measurement your facility uses, as meters are slightly longer than yards, and if you key in the wrong measurements, the Fitbit will auto detect your swim exercise and give you inaccurate stats. For example, keying in 25 meters when the pool length is really 25 yards will make you seem slower, coz the Fitbit "measures" your flip turns or change of direction at each end of the pool. I have both a Charge 3 and a Flex 2, and have had no problems with both tracking swims accurately. Just remember to swipe up on the Charge 3 and press the "start" and "finish" buttons. Calories burned depends on how fast you swim. The faster you go, the more calories you burn. But it's hard to keep the speed up consistently during a swim, so maybe do some quick sprints and continuous slow swims in succession, one right after the other, because I've noticed that if you stop for even a few seconds to rest, the Fitbit also stops tracking, then you have to restart on the Charge 3 again. For this reason, I love to consistently use my Flex 2 for swims because I don't have to do a restart, but it will just auto detect a new set of laps for my slow swims and my sprints.
