Last year Misfit and Speedo partnered to add swimming features to the Shine fitness tracker. It worked well enough that they are doing it again.
The Misfit Shine 2 is properly waterproof - IP ratings are only about submersion, not the rigors of swimming. They can also track your swim, including the distance (accurate to a meter, Misfit says) and counting your laps. Alternatively, you can set a timer if your exercise program is time-based.
This is in addition to the usual terrestrial activity tracking. You can also use the Speedo Fit app for a more insight into your exercise.
The Misfit Shine 2 Swimmer's Edition will retail for $120, $20 over the regular Shine 2. It will launch in the next two or three weeks.
If you already bought a Shine 2 (or Ray) fitness tracker, you can still get the new features - as a $10 firmware upgrade (available in July). If you're thinking of saving $10 getting a base Shine 2 and upgrading, note that the Swimmer's Edition comes with an extra strap (which accounts for the $10 difference).