I'm struggling to understand how Garmin can market the Instinct 3 as a capable multisport and swimming watch when I'm seeing results like this.

Over the last few weeks I've done several very similar pool sessions:

1200 m

Around 31–32 minutes

Same swimmer

Same pool

Same wrist

Similar pace

Similar perceived effort

I compared the results from three Garmin watches:

Forerunner 970

Zone 4: 38%

Zone 3: 43%

Zone 2: 16%

Zone 1: 0%

Fenix 8 Pro

Zone 4: 37%

Zone 3: 25%

Zone 2: 22%

Zone 1: 12%

Not identical, but broadly consistent. Both indicate a moderately hard aerobic workout with significant time spent in Zones 3 and 4.

Instinct 3

Zone 4: 0%

Zone 3: 0%

Zone 2: 37%

Zone 1: 61%

According to the Instinct 3, I spent essentially the entire swim jogging through a warm-up.

That simply makes no sense.

Either:

The Fenix 8 Pro is wrong.

The Forerunner 970 is wrong.

Or the Instinct 3 is wrong.

When two independent Garmin flagship watches tell a similar story and the Instinct 3 tells a completely different one, it's hard not to conclude that the Instinct is the problem.

What frustrates me is that Garmin's marketing gives the impression that the Instinct 3 is a fully capable sports watch, not some entry-level device that should be expected to produce wildly different physiological data in the pool.

If optical heart rate during swimming is not reliable on the Instinct 3, that's fine. No wrist sensor is perfect in water. But then Garmin should be transparent about that.

A difference of a few beats per minute is one thing.

A workout that is mostly Zone 3/4 on two watches becoming almost entirely Zone 1/2 on the Instinct 3 is something else entirely.

At this point I'm seriously questioning whether the Instinct 3 can be trusted for heart rate tracking in the pool at all. 

Swimming instinct 3