Open water swim tracking relies on GPS — not lap counting. The accuracy and features available depend heavily on your device and how you set it up. Here’s what you need to know.
Why Open Water Tracking Is Different
In a pool, your watch counts laps and calculates distance from lap count × pool length. It’s consistent and reliable (once calibrated correctly).
In open water, there are no laps. The watch uses GPS to track your position every second and calculates distance from the GPS path. This is much more variable — GPS signals, arm movement, and swimming stroke all affect accuracy.
Device Recommendations for Open Water
Apple Watch Ultra 2: Currently the most accurate consumer device for open water swim GPS. The dual-frequency GPS and improved algorithms produce tight, accurate tracks. Recommended for serious open water swimmers.
Apple Watch Series 10: Good GPS in open water. Some path smoothing in the algorithm — slightly less raw accuracy than Ultra 2 but adequate for training.
Garmin Forerunner 965 / Fenix 8: Excellent open water tracking, multi-band GPS, very accurate. Garmin’s algorithms are well-proven for open water.
Garmin Swim 2: Basic GPS in open water — functional but less accurate than Forerunner/Fenix models.
Setting Up Your Watch for Open Water
Apple Watch:
- Select “Open Water Swim” workout type (not Pool Swim)
- GPS will activate automatically
- Ensure location services are enabled
Garmin:
- Select “Open Water Swim” activity profile
- Enable GPS (and multi-band GPS if available on your model)
- Disable pool length settings for open water sessions
Key setting: Make sure you’re using the correct activity type. Pool Swim mode on Apple Watch doesn’t use GPS — it uses the accelerometer. If you select Pool Swim for an open water session, distance will be inaccurate.
What Data You’ll Get (and Its Accuracy)
Distance: Accurate within 2–5% on modern GPS devices. GPS tracks your actual path — if you zigzag, it measures the zigzag distance, which may be more than the straight-line distance.
Pace per 100m: Calculated from GPS distance and time. Less precise on a stroke-by-stroke basis, but accurate for overall session pace.
Route map: GPS track of your swim plotted on a map. Useful for reviewing navigation efficiency.
What you won’t get: Stroke count, SWOLF, and per-lap splits aren’t meaningful in open water. Focus on overall distance, pace, and time.
Logging Open Water Sessions
After your swim, review:
- Total distance vs. straight-line distance (the ratio shows how well you navigated)
- Overall pace per 100m
- Total time
Log these in SwimBeat or your training app alongside your pool sessions. Building a training history that includes both pool and open water helps you understand your overall fitness progression.
Tips for Better GPS Accuracy
- Swim freestyle — GPS chips in smartwatches activate during the hand’s aerial recovery phase. Freestyle provides the most consistent GPS signal acquisition
- Don’t cover the watch face during the swim (some wetsuits have tight sleeves)
- Wait 30–60 seconds after selecting your workout for GPS to lock before entering the water