What is the maximum underwater depth supported by the fenix 7 ?

Although the water rating of Fenix 7 is 10 ATM, and the description claims "Withstands pressures equivalent to a depth of 100 meters", the watch is not supposed to be used for scuba-diving. Only "splashes, rain or snow, showering, swimming, diving into water, snorkeling, high-speed water sports" are covered by the guarantee. The F7 will likely survive an occasional dive to 40m, especially if you avoid pressing buttons at depth. However, if it suffers a water damage, it won't be covered by the guarantee.

Water Rating Definitions | Garmin

To add to what Trux says (which is all correct), I just want to add that in all my years on Garmin forums and user groups I don't recall ever seeing a report of a Fenix sustaining damage from water pressure. Personally I would err on the side of caution, as Trux recommended, although I probably wouldn't hesitate to take mine down to 20-40 meters once in a blue moon. But realistically it's probably not going to have any issues. That said, in the off chance that something somehow did occur then Garmin probably wouldn't honor the warranty.

If diving to 20+ meters is something you plan to do regularly, I'd recommend a Descent MK2 which is actually designed for that and is FULLY rated for a diving depth to 100 meters. Even if you won't actually use the dive features, just the added level of water pressure protection is worth it. Also it has all the Fenix 6 features, software-wise (though they haven't made one with fenix 7 hardware yet unfortunately)

It's funny. The only stated difference in WR between the Fenix and the Decent is that the Decent is tested to an Engineering standard that has nothing to do with WR, it's a diving depth gauge standard. 

It says it's water resistant to 100m, then it should be WR to 100m with ordinary use. 

"Her Deepness" regularly dives with a Rolex Datejust which only has a WR of 100m 

www.rolex.org/.../an-ocean-of-hope

Water resistance of 10 ATM means the watch was tested for that pressure statically. It does not involve any movement, or manipulation of the watch, using buttons, tapping on the watch, or smaller shocks - all of that can easily happen during a dive, and nothing of it has been tested against. The watch is simply statically tested for 10 ATM, but is not certified or covered by the warranty for scuba diving. That's the standard across the watch industry as you can see also in the WikiPedia article about the Water resistance classification:

Water Resistant mark - Wikipedia

Moving a watch underwater isn’t relevant. Movement creates dynamic pressure. You can’t move your arms fast enough under water to create a material change in pressure. https://www.watchuseek.com/threads/sigh-myth-busting-again.610734/  The same probably applies for any underwater bumps.

Is there any difference between scuba diving and free diving, noting the World Record for free diving is over 100m?

All I’m saying is the watch should be fine diving to 100m if it’s certified to 100m. I would expect my 100m water resistant watch to be work to that depth (noting PADI’s deep diving certification is only to 40m). Realistically though, if I got to 100m deep, I’d have more concerns than whether my watch was working as it would probably be part of a one way trip.

RobinNZ said:

You can’t move your arms fast enough under water to create a material change in pressure.

It is not about changing the pressure. It is about reducing the waterproofness of some seals when using / manipulating / moving / shocking the watch vs. the static situation used during the 10 ATM testing.

The watch is simply not tested and not covered by the warranty for scuba diving. Regardless whether the watch withstands it or not, and regardless what you think about. You do not have to obey, and you can dive with it, but do not expect the warranty if something goes wrong.

Garmin warranty policy doesn’t cover any water damage so regardless of which watch you use (even the decent), if it breaks, you’re stuffed. 

Setting that aside, I would argue differently 100m is a definite metric. It can be reached diving or swimming (in theory). Whether you have a tank on your back can’t be the metric. If scuba diving is the metric, your argument is that if the watch fails while learning to scuba in your local swimming pool at 1.5m deep, then you’re out of warranty. 

Either way, I do take your point on risk. If you use something (watch under water or otherwise) and it fails, there is a risk that the manufacturer won’t accept a warranty claim. 

RobinNZ said:

Garmin warranty policy doesn’t cover any water damage so regardless of which watch you use (even the decent), if it breaks, you’re stuffed. 

Where did you see that? If you manage to have a leak at a Descent during a common scuba dive, I am sure it will be replaced promptly.

RobinNZ said:

Whether you have a tank on your back can’t be the metric.

It is not about the tank on the back, it is about the usage of the watch at depth. For example pressing a button that was not designed to be pressed underwater, may lead to a damage. MK1 / MK2 / GI1 have different buttons, as far as I could see, than other Garmin models. 

https://www.garmin.com/en-US/legal/consumer-limited-warranty/

Usage is different if your swimming vs diving but my point about the tank stands. The depth is the relevant differentiator and the Fenix says it can go to 100m. 

Anyway, we’ve probably gone way deeper (pun intended) than the OP wanted. It’s after midnight here, my game has just finished so I’m off to bed. All the best. 

Personally, over the years, I have regularly used plenty of water resistant 100m watches including automimic and  quartz Citizen and Seiko watches also the Fenix 5 and 6 for dives to 40m and never suffered any kind of failure. I have not used the Fenix 7 for diving as I have not dived since the start of Covid, but would not hesitate to do so.

Having said that I avoid using the buttons at any time in the water and would not expect a warranty claim to be accepted if I was using it whilst scuba diving. The current Descent range features inductive charging and the buttons operate by inductive technology which means that the case is effectively sealed. The descent is in compliance with the EU standard EN 13319 (as is the Apple Watch Ultra apparently) which means that it is certified for recreational scuba diving to 40m and as such, scuba diving should be covered by the "during normal use" clause in the limited warranty.

I have a Suunto Dive computer but if I didn't and wanted dive computer functionality from a smartwatch I would buy the descent without any qualms.