In Final Fantasy XIV, players could fly before they could swim. There’s no joke there. The game’s first expansion added the ability to fly through the expansion zones on a mount, but it was the second one that added the ability to swim anywhere. And there are still a lot of places where there are bodies of water you can’t swim in, or spots wherein you can see beneath the water’s surface but not descend to explore it.
This is not really a fault of the game, per se. Lots of games have gone in on underwater content, including Guild Wars 2 offering a pretty developed underwater combat system and World of Warcraft even giving us an entire underwater zone. Yet somehow underwater stuff keeps being kind of… haphazard. It doesn’t seem very well developed and tends to get shoved off to one side and also people hate it. Why is that? Well, I can think of some reasons. A good list’s worth, even.
1. Some MMOs are exempt just by concept
Look, let’s be realistic right off the bat. Some games make no sense going underwater. Auto Assault could never have really featured you driving your car into underwater areas because if you drive your car into a lake you are now down one car in the best scenario. There is no situation where the titanic spacecraft of EVE Online could slice their way into deep waters, recalibrating weapons as they seal against new pressures before jumping backing into space and…
Wait, what was I talking about? That sounds awesome. But it’s still not going to happen.
2. Humans cannot breathe underwater
I know, in many games you are not playing a human. However, even in those games your fantastical races generally operate the same way as human beings do, with a few rare exceptions when it comes to underwater life. The net result is that any underwater content has to immediately deal with the fact that your character cannot breathe and thus has immediate restrictions on operations.
The usual result is giving characters somehow more lung capacity than most normal humans even as you still watch your breath meter decrease, and I do not want to imagine what it’s like to play that as someone who has a deep fear of drowning in real life. Heck, even just people with traumatic memories from Sonic the Hedgehog.
3. Interesting environments are even harder than with flight
One of the big problems with designing zones that are still neat when players can fly is, well… flight means that you can just go up and over most obstacles. Underwater, this issue is compounded. It’s not that everything and everyone can fly, it’s that three-dimensional space is easier to move in all directions even once you fix the breath issue.
Often, this means forcing you to swim into shipwrecks or narrow cave systems, which means that you immediately are stuck in claustrophobic spaces that are difficult to navigate and about as clear as mud even as you try to find which way is up. This is not conducive to fun times.
4. Fighting requires special consideration
Underwater regions mean that every single combat encounter now has to take careful note of elevation in addition to other facts when managing positioning. It also involves dealing with the fact that water does not behave like air  and thus will affect things like fire magic, electrical abilities, blunt weapons, projectiles, and so forth. There’s a reason that GW2 basically designed a whole separate weapon system for when you’re underwater.
5. Moving in water is slower
All of these facts are usually present in single-player games with underwater segments, of course; often these segments are just as loathed by players. They exist as equalizers in a way, forcing you to contend with environments that obey different laws from the majority of the game’s content and fighting things that move naturally while you are hamstrung.
Yes, some of this slowness can be mitigated with fun things like seahorse mounts or riding dolphins or whatever. But you note how these things are added to make underwater content feel less like underwater content. Which points to a problem…
6. The suspension of disbelief gets harder
I am absolutely never going to strap on a full suit of plate armor and charge at someone with a sword. Most people probably won’t. I’m never going to be able to fly under my own power, I probably won’t be able to shapeshift into a bear, and I place low odds on the likelihood that I will one day be able to teleport. But I have been underwater, and that is not terribly unusual; swimming pools alone give us a basis for understanding about what being in water is like.
This is where the suspension of disbelief gets a little bit harder. It’s not overwhelming most of the time, but it’s easier to believe in something unrealistic when it’s an experience we haven’t actually shared. Heck, an awful lot of people in Victorian times died just by falling into water wearing heavy clothes that got soaked. I know how hard it is to swim in what is basically a piece of underwear; it’s harder to believe that I could just as easily move in a floor-length robe while fighting off fish with a pair of swords.
7. Awkwardness isn’t fun
I always did kind of like the way that alcohol impaired movement and visuals in WoW, and I still do to this day. It’s a neat bit of verisimilitude, making the game just a little bit harder to play if you decide to imbibe. Of course, the flip side is that your choice to use alcoholic beverages in the game is… well, a choice. Having to go underwater for a quest that requires it is not a choice except insofar as you can opt to not do it at all, and that may not be a realistic option.
Imagine if for a given quest you had to get absolutely smashed and then had to deal with it for several quests. You probably wouldn’t think of that as a fun moment. Awkwardness forced on players is generally unwelcome.
8. Everything is different (and that’s hard to model)
By now, I think the point has been made. Underwater content is not just “above-water content but with more water.” What you really need to do in order to make this content work is to design entirely different mechanisms to navigate, fight, explore, survive, and so forth. In other words, you need to design the game for two different systems from the top down.
The game that has gotten the closest to doing this is Star Trek Online, which has two completely different ability layouts for space and ground combat. Go ahead and ask players if that means both sides are equally beloved. Seriously. Ask.
9. It’s not universal
Even if you do all the work to make the best underwater content possible within your MMO so that everyone can enjoy it, the simple reality is that “lakes/oceans full of quest objectives” are a distinct minority of the game world. For a lot of the game, players will probably be in the world of surface and air because, as mentioned, humans live there. We live above the surface of the water. We don’t breathe underwater.
So do you really want to spend all that time designing underwater content when it’s not even going to be the primary way of interacting with the world?
10. Fishing is easier
Yeah, fishing. You throw a line in and catch a fish. There, we’ve justified all the bodies of water out there. 10/10, we have found something good about fishing after I have spent years dragging it. Congratulations, fishing, you’re sort of all right in this one particular circumstance I guess.