Small diving trip. What activity to use?

From the Owner's Manual:

Swimming

NOTICE

The device is intended for surface swimming. Scuba diving with the device may damage the product and will void the warranty.

NOTE: The watch has wrist-based heart rate enabled for swim activities. The watch is also compatible with the HRM-Pro , HRM-Swim , and HRM-Tri accessories. If both wrist-based heart rate and chest heart rate data are available, your watch uses the chest heart rate data.

To clarify, I’ll be 20-30 feet under the water. The watch is waterproof and should be able to handle that. 

Josh said:

I don’t really see a relevant activity 

because

gaijin said:

Scuba diving with the device may damage the product and will void the warranty.

Josh said:

The watch is waterproof and should be able to handle that

And well it might but Garmin suggest you don't dive with it. It's up to you.

https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-7-series/313351/can-the-tactix-7-pro-be-used-for-diving

It's up to you. If your watch dies, you'll have to buy a new one. 

Josh said:

Any ideas what to use instead? I don’t really see a relevant activity

If you want to take the risk of the water damage voiding the warranty, use for example Open Water Swimming, and then change it to one of the Scuba Diving types, or to Apnea (if freediving), in Garmin Connect. That's what I do when diving or freediving with my Instinct 2.

Avoid pressing the buttons when underwater.

Without continuing the conversation of whether the watch can or cannot work while diving, I’ll give you my personal thoughts.

During the dive, the watch will not give you any useful information other than time, and since it can’t be used as a dive computer you will (should) already have a separate dive computer or other devices to track depth, time, NDL time remaining, etc. Therefore, I take my Epix off and leave it on the boat.

I do, however, use the Boat activity on the Epix to track the dive start location and pick up location, and then I use the Garmin Dive app to manually record the details of the dive from my dive computer plus the entry and exit point I recorded on the Epix. Using the Garmin Dive app puts the activity in Garmin Connect as well.

I am considering getting a Descent G1 to use while diving, but I haven’t pulled the trigger yet. 

I do not understand why Garmin cannot just add $5 to improve the seals and allow Fenix / EPIX / Tactix / Enduro owners to do recreational diving a few times per year. Isn't this supposed to be a top-of-line-rugged-outdoors-track-every-activity-watch? Even the relatively toylike Apple Ultra has this capability (despite also having 3 microphones plus an 86dB speaker). Imagine the advertisement where dude removes his $2500 Marq 2 Captain (a friggen tool watch built for the SEA!) for a 60 foot dive in Bermuda, replacing it with an AWU!?! Or a Navy seal operator rendezvous with submarine by parachute "standby team. I have to remove my Tactix 7 because Garmin will void the warranty"

ericgottlieb said:

During the dive, the watch will not give you any useful information other than time, and since it can’t be used as a dive computer

Well, that is definitely true right there. 

its not just $5 on the seals - it is also changing the button design to inductive buttons etc.

But yes tend to agree with you that it would be nice if these watches were rated to that level as long as it doesn't buik out the case/weight by more.