I just swam 1400m with the Apple Watch Ultra 4 and Garmin Fenix 9 Pro: Here’s which watch came out on top, and it wasn’t the one I was expecting

The Apple Watch Ultra 4 and Garmin Fenix 9 Pro are both top-of-the-range watches, with all the sports modes and stats you could need to track workouts. I’ve been testing both since they launched earlier this year, and I ran a marathon with both watches on my wrist a few weeks ago.

Next up, I wanted to see how both watches performed in the water. To find out, I strapped a watch to one wrist and used my Speedo iQ Vanquisher 3.0 goggles to measure how far I swam and how fast. When I got back on dry land, I downloaded all the data to see which watch came out on top — read on to find out more.

I just swam 1400m with the Apple Watch Ultra 4 and Garmin Fenix 9 Pro: Here’s which was more accurate

Let’s start with how these trackers measure your swimming workouts. Both use an internal accelerometer and gyroscope to recognise arm pulls and calculate how many strokes you take per length, as well as your stroke rate (strokes per minute). Both watches are waterproof to 10m, do automatic stroke detection, and can give you a SWOLF score — a measurement of stroke efficiency.

There’s a slight difference in usability between the two watches in the pool, namely down to the watch design. The Garmin Fenix 9 Pro has five leakproof buttons — three on the left, two on the right — which make navigating the watch in the pool a dream. The Apple Watch Ultra 4, on the other hand, locks the screen when you’re in the pool, so you’re relying on the Action Button to pause your workout, but you’ll have to deactivate the Water Lock to stop your swim.

As a control, I used my Speedo iQ Vanquisher 3.0 goggles. These smart goggles give you a wealth of data when you’re back on dry land. As well as your pace, distance, and how long you spent resting at the side of the pool, you can also see your head position, breath time and distance per stroke for each stroke.

Here’s the data:

I recently did this same test with the Apple Watch Series 12 and Fitbit Edge, and the Apple Watch won. Looking at the data, the same is true for the Apple Watch Ultra 4, which was, once again, spot on during this swim.

The Garmin Fenix 9 Pro recorded an extra 40m, which is only two lengths of the 20m pool I was swimming in, so it’s not in any way inaccurate, but just not quite as close as the Apple Watch Ultra 4.

Looking at the stroke breakdown in the Garmin Connect app, the Fenix 9 Pro also seemed to randomly mix up strokes, finding it harder to differentiate between freestyle and breaststroke. This led the watch to largely record my swim as "Mixed," rather than giving me a proper breakdown of each stroke.

Again, there’s not an awful lot in this, but it’s worth highlighting how accurately the Apple Watch Ultra 4 performed here. In the water, I definitely found the Garmin Fenix 9 Pro easier to use, plus you can connect the Fenix 9 Pro with a compatible HRM Swim chest strap, whereas you can’t do the same on the Apple Watch.

I’ll continue testing both watches, so stay tuned, but which would you pick between the two? Let us know in the poll below:

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