[Guide] Underwater Cave Mining (1.81.1)

Ever since 1.18 dropped for the first time, what was once a rarity is now fairly common. And finding a good underwater cave system can be just as rewarding as strip mining with DCs of various ores awaiting harvesting. This is how you can reap the riches of the ocean and return with ore filled pockets.

The topics I'll cover here are as follows:
Equipment (And why)
Setup
Dangers
Tips

First off: Equipment

Potion of Water Breathing (8:00) (WB) - With how uncommon magma blocks are, this is an absolutely necessity to bring with you as you'll run of oxygen quickly underwater.

Potion of Night Vision (8:00) (NV) - Trying to see without this potion is impossible. It is as required as the Water Breathing potion.

Potion of Fire Resistance (8:00) (FR) - This is optional, but very nice to have in case you bump into underground lava pools. Better to have slightly less inventory for mining rather than mounting an extremely difficult recovery mission. (I know this based on experience)

Sword (preferably enchanted) - This will be your main defense against Drowned, since a bow's range, even at max charge, is very short.

Pickaxe (Iron at minimum, maxed out) - Your main mining tool. Yes, you will slower underwater, but Efficiency does help reduce the penalty. Fortune will have you rolling in harvested ore. And Mending keeps your pickaxe at full health if you mine ores that drop experience orbs. You should have Unbreaking on everything anyway.

Shovel (Maxed out) - This is optional, but gravel is pretty common in both the deep ocean and in underwater caves.

Food - Do I really need to say anything here?

Shulker Box(es) - Optional, but the more ore you can lug back, the happier you'll be. Plus, if you want to spend a long time

That is all the equipment you'll need. No torches needed as your NV potion will be all that you need in that regard.

This is how my setup works. Yours can be different according to preference.



The 4 potions in the top left are Night Vision potions while the middle left potions are Water Breathing. My hotbar is as follows: Sword, Pick, Shovel, Food (With more above), NV potion, WB potion, FR potion, Shulker Box A (contains 13 NV and WB potions and 1 FR potion), and Shulker Box B (with Shulker Box C above, both used to store the ores).

This is not a task without dangers. You can easily die and face a difficult recovery operation if you're not careful. Here are the dangers with their risk factor.

Drowned - Slight Risk - Without tridents, they are no threat. With tridents, since you have no bow, they pose a major risk since they a ranged attack and you don't (Armor reduces this risk, but not by much). Strafe from side to side to dodge their attacks and slice them with your sword. Repeat until they're dead.

Drowning - Slight Risk - This is an obvious one but an unlikely one for 2 reasons. One are those mandatory WB potions. The other is Tip 6 (See below).

Fall Damage - Moderate Risk - When mining ores, you might breach into a normal cave. Depending on the layout, you could face a long drop which will kill you. Stay in the water and you'll be fine.

Hostile Mobs - Moderate Risk - If you breach into a normal cave, it won't be be lit. Therefore, take precautions as you would normally cave mine on the surface. Skeletons will be your biggest threat. Avoid them if possible. Remember, underwater caves are perfectly safe with the exception of the occasional Drowned.

Lava - High Risk - You can harvest ore right into a massive lava pool, and since swimming in lava is identical to swimming in water, those swimming mechanics will likely betray you and get you killed. I know this from personal experience. If you find yourself in that situation, pop a FR potion and use the time it buys you to either escape from the opening or dig yourself out.

Finally, here are some tips and tricks to make your trip easier and safer.

1. Avoid Underwater Temples - The Guardians will inflict Mining Fatigue, making mining underwater impossible. Besides, you're here for ores, not sponges.

2. Dolphin's Grace is your friend - Although it is short lived, the speed boost will allow to cover more seafloor ground quickly, allowing you to find those caves quicker.

3. Drink your NV Potion before your WB Potion - If you drink your WB first, you won't have a good indicator that you're running out of time. Drinking a NV potion will cause your vision to flicker as it runs out, which can also be used to warn you that your WB potion is also running out.

4. If possible, avoid drinking you potions underwater - If you drink them underwater (unless you time it right), you run the risk of replacing the potion with a water bottle instead of an empty bottle. You can't stack water bottles, unlike empty bottles, which clutters your inventory.

5. /trash is your constant friend - You will sometimes have to collect things like cobblestone and deepslate. You're here for ore, not that, and it'll clutter you inventory. /trash will easily get rid of them for you.

6. Return if your supplies get low/If your inventory is full - You wouldn't keep pushing into an unexplored cave without torches or keep digging with a full inventory, right? Same logic applies here as well except this time you have potions to worry about for the former. This is common sense, but I feel like hammering the point home here since I doubt any of us want to be that guy who dies from running of supplies.

7. Be aware of your surroundings - Same as cave mining on the surface. Hear lava? Don't dig near it if you can pinpoint its location. This stuff is common sense as well, but dying stupidly because you weren't paying attention is not fun. I know this from experience.

8. Pick the right Outpost - This goes without saying, but your starting point should either be near or in the ocean. If you going to walk hundreds of blocks just to get to the ocean, you might as well cave mine on the surface. Also mark their coordinates so you know where to go once you're done mining.

That should be everything you need to know about underwater mining as of the current build (1.18.1). Feel free to ask questions, add further points, and critique my work! Have a nice day, guys!

I do a decent amount of underwater activities, and I find of invaluable assistance the three enchantment: depth strider 3, aqua affinity, and respiration 3. They make it just as easy to operate as being on land.
Also, to add to your list, torches on EMC don't break when they are placed under water, so you can use them as very accessible air pockets. They're safer than magma blocks, and you can break them and take them with you when your air is full.

To add onto the setup, you can also use a helmet with Aqua Affinity and/or Respiration (preferably both) & leggings with Depth Strider. With those three together, you can mine & move underwater faster, plus it'll take longer for your respiration bubble meter to decrease.

And, for those who don't really have access to potions (i.e. new players), bring some torches , chests & a bed and dig into one of the walls and make a little base camp out of it. Make sure to block the water from flowing into your camp.

That's what I said...