Apple Watch Ultra 3 beats Garmin Forerunner 970: GPS Accuracy in OWS

I snuck in a quick open water swim test today of the new Apple Watch Ultra 3, the GPS track was a bit better than the Garmin Forerunner 970. The HR track? Less so! Here are the test results’

Test Conditions and Equipment

There was clear open sky on a cool but sunny day. It was a delight to swim a lap of the lake, and the water is starting to cool down, perhaps sitting around 18 degrees Celsius.

I wore the Watch Ultra 3 and Forerunner 970 on each wrist with my wetsuit sleeves rolled back for the photos, but pushed further up the arm and covered by the wetsuit material. I had a Garmin HRM 600 chest strap separately recording an HR track and a Polar Grit X2 in my pool buoy as a reference track. The Workout app recorded the track on Apple using dual-frequency GNSS, and the Forerunner 970 was set to use SatIQ (L1+L5 on demand) and the Elevate 5 optical HR sensor. With Polar LOOP on one biceps and Whoop on the other, I was ready to go.

It was about 15 minutes of swimming, and I was already warmed up from other activities.

GPS/GNSS Accuracy Test Result –

Apple Watch Ultra 3 more closely follows the reference track than the Garmin. Garmin appears to smooth the track and gives me more credit for swimming in a straighter line than I probably did! That said, the starting straight (right side) sees the Garmin track deviate slightly inward toward the centre of the lake, and my fading memory tells me that’s what I might have done, yet the other two tracks disagree. Further on in the swim, the Apple and reference track match my memory.

Garmin recorded a seemingly accurate lap distance at 12m over (762 vs 750). Oddly, Apple was 20m over, but I may have made a slight mistake with the lap press; the Apple lap clearly looks shorter based on the track.

I’m also not entirely sure that the official lap length is correct, as the buoys are in a different place than in previous years.

I am happy with the Garmin and Apple here

Open Water Swim Heart Rate Accuracy Test

The test results here are all over the place, with none agreeing with the reference track. Apple perhaps looks the closest to the reference track, but then had two notable dropouts, which made the results unacceptable; the other were all about right.

 

Apple Watch 3 Swim Accuracy – Take Out

Apple Watch Ultra 3, like its predecessors, has an unhelpful knack of periodically losing heart rate data. I found something similar in a running test yesterday, although nowhere near as bad as today. I suspect apple chooses not to record data that its sensors flag as bad.

The GPS tracks today were great. Compared with open-water swim tracks from 5 or more years ago, today’s crop of watches is greatly improved.

Apple Watch Ultra 3 – Raw Data Accuracy – is it better than in the Workout app?

 

 

 

 

 

Last Updated on 10 March 2026 by the5krunner