How to Choose and Use a Smartwatch or Tracker for Swimming

A smartwatch or fitness tracker can record swimming well enough to be useful, as long as you know where it is reliable and where it is not. Pool swimming is the strongest case, since lap counting works well once the pool length is set correctly. Open-water distance, heart rate and touch controls are weaker, and most disappointments come from expecting them to match a pool session.

How swimming modes work

Swim modes use the motion sensors in the watch, usually an accelerometer and a gyroscope, to detect arm strokes and the turn at the end of each length. The watch counts a length each time it sees a turn or a push-off from the wall. From those counts it works out distance, pace and an estimate of calories.
Stroke detection is most consistent for freestyle, which is the most regular movement. Backstroke, breaststroke and butterfly change the arm pattern, so detection is often less steady. Kick-only sets, pull buoy work, drills and resting at the wall can be counted as swimming or missed entirely.

The practical result is that a session with mixed strokes can end a few lengths off. Compare the watch's total with your own count for a few sessions to learn how it handles your stroke.

Setting up pool mode

Before the first session, set the pool length to match the pool you use. Pools are not all the same length, and a wrong setting skews distance and pace together. Check the sign at the pool or ask the staff instead of guessing.
Start the pool swim activity before you get in, so the timer and lap count begin with your first length. Turn on water lock, or the closest equivalent, before you enter the water, and use the physical buttons to pause, end or mark a rest. If you train with structured sets, learn the interval or drill options at home first, because menus are hard to read with wet hands and goggles on.

Open-water swimming and GPS

GPS signals do not travel through water. A watch with GPS gets a position while the wrist is above the surface, and between those fixes it estimates where you went. For open-water swimming, route, distance and pace are approximate, and waves, currents, sighting and turning at buoys all add error. The limits of GPS accuracy on land apply here too, only more so.
Use the open-water mode if the watch offers one. Pool mode assumes a fixed length and a wall at each end, so it cannot follow a route. Treat the recorded route as a rough record rather than a precise course, and test it on a familiar shore or lap before you rely on it for a longer swim.
A watch cannot provide open-water safety. Swim with a buddy or a lifeguard present where possible, and keep your attention on the water rather than the screen.

Heart rate and other sensors in water

Heart rate is harder to measure in water than on land. Optical sensors read blood flow through the skin, and water movement, cold temperature and a loose strap all make that signal noisier. Cold water also narrows the blood vessels near the skin, which weakens the reading further. Expect gaps and sudden jumps during a swim, even on a good watch.

Treat swimming heart rate as a rough trend across sessions, and compare workouts done with the same strap fit and similar water temperature. Heart rate accuracy on the wrist covers the sensor limits in more depth.
Some watches can pair with a chest strap for swimming. Support varies between models, and radio links do not always hold well underwater, so check the manual before you depend on it.
Other sensors are generally not meant to be read during a swim. Blood oxygen and stress or recovery readings are best ignored until you are out of the water.

Battery, strap and fit

Open-water GPS, continuous heart rate and a bright, always-on display all drain the battery faster. A long open-water session can use a large share of a charge, so start with a full battery and check any estimate the watch gives for a long swim. Everyday battery habits apply here too.
Silicone and similar rubber-like straps are the usual choice for swimming. Leather soaks up water, dries slowly and does not cope well with chlorine or salt. Fit the strap so the sensor sits flat on the skin without digging in, because a loose band lets the sensor move and a tight one becomes uncomfortable on a long swim.
Rinse the watch and strap under fresh water after every pool or sea session, then dry them thoroughly. Salt and chlorine residue can dry on straps and around the buttons, and can stiffen rubber over time. The full routine is in the water resistance guide.

What to compare before you buy

If swimming is your main use, compare the points below. Features differ between models and generations, so confirm each one in the manual or on the product page rather than assuming.

FAQ

Does a smartwatch track swimming without a pool mode?

Some watches detect swimming automatically, but distance and laps are usually less reliable without a dedicated swim activity. Start the swim activity every time you get in the water, so the watch knows what it is measuring. Automatic detection is useful for a rough record of an active day, not for a training log.

Does GPS work underwater?

No. GPS signals do not pass through water, so the watch gets a position only at the surface. The route between fixes is an estimate, which makes open-water distance approximate.

Can I use the touch screen in the pool?

Often not reliably. Turn on water lock, or the equivalent, before you swim, and use the physical buttons to pause, end or move between screens.

Is the heart rate reading accurate in the pool?

Treat it as a rough trend rather than an exact figure. Water, cold temperature and loose straps all make optical readings less stable, so compare sessions done under similar conditions.