curious if spells act as thier natural counterparts or if they have thier own reactions due to it bieng magic

Fireball would not work underwater.  Granted there is nothing in the rules about it but it sounds like common sense.

It would be up to the DM

Fireball actually works fine underwater. The spell text does not say anything about the spell not working in water.

However, creatures in water DO have resistance to fire damage. So a fireball spell used underwater would operate normally but creatures would take half the damage after the save because they are resistant to fire damage underwater.

Quote from David42 >>

Fireball actually works fine underwater. The spell text does not say anything about the spell not working in water.

However, creatures in water DO have resistance to fire damage. So a fireball spell used underwater would operate normally but creatures would take half the damage after the save because they are resistant to fire damage underwater.

 conversely it also does not say it will work under water.  It is a detail that has been overlooked. 

However, it does have a verbal component which may not work underwater.  And the bat guano may dissolve and the sulfur float away.

1) By default, spells work. Unless something explicitly negates this, there is no reason to assume otherwise.

2) Players that are holding their breath have enough air to cast one spell. If they do so, they immediately begin suffocating.

3) Sure, there are some specific practical complications, but there are many ways to cast spells, and the bottom line is that they do work underwater. In a world of magic, nitpicking minutia is likely to reduce the overall enjoyment of the game.

Casting spells underwater is a different question from what happens if a fireball is cast underwater.

If you can cast spells underwater then fireball works as I described. Creatures in water have resistance to fire damage.

As far as whether spells can be cast underwater or not. That is entirely up to the DM. The rules say nothing about it. They do say if you are gagged or in a region of silence or similar then you can't perform the verbal component of spells. Being underwater isn't mentioned.

Since the rules do NOT impose any restrictions on casting underwater, some DMs may choose to do so.

Most DMs rule that if you can breathe underwater then you can cast spells with verbal components underwater. If you can't breathe underwater then the DM can decide however they like. RAW there is NO restriction on casting spells with verbal components underwater,  so it is up to the DM to decide how they want to run it. The rules don't impose a restriction so if the DM wants to impose one that is up to them.

P.S. As for your comment about material components, since no cost is associated with these, the spellcaster can use an arcane focus like a wand, orb, staff, amulet or similar as the material component. So the only question remaining is whether the caster can use spells with verbal components underwater or not and that is entirely up to the DM.

One house rule is that, if a character can't breathe underwater but is holding their breathe then they can manage to cast one spell with a verbal component but after that they have expelled all their breath and start drowning but that would be a houserule/DM ruling. So if you have a question about casting spells underwater, the best answer is Ask your DM how they plan to run it.

P.P.S. The rules just do what they say they do. There aren't "overlooked" details in cases that disagree with how you might choose to run it.

[Sageadvice]

now, see, I have a rock paper scissors thing with my magic that falls under the "elemental" (as opposed to the dimensional) tht says no, fireball does not work underwater.

However, if the magic feels like being a PITA, casting a fireball causes it to turn into a big ole bubble of space and sound, which can be quit dmaging.

It all comes down to the individual rules of magic for the table (ie, the DM).

Quote from Kotath >>

Quote from AEDorsay >>

now, see, I have a rock paper scissors thing with my magic that falls under the "elemental" (as opposed to the dimensional) tht says no, fireball does not work underwater.

However, if the magic feels like being a PITA, casting a fireball causes it to turn into a big ole bubble of space and sound, which can be quit dmaging.

It all comes down to the individual rules of magic for the table (ie, the DM).

 

So... if fire does not work in water, does that mean earth does not work in air? 

Don't ask me hard questions! I'm a DM, not a lawyer! I only write the stuff...

Also, turns out that I may have been wrong...

... or not, since fire needs oxygen to burn and given how The Pale is, it would probably allow it on some occasions, but only after converting a lot of water to the oxygen necessary via lightning (thus electrocuting all the people in the range as well), and supplying extra hydrogen as well for an even bigger boom.

Quote from Memnosyne >>

[Sageadvice]

No rule prohibits verbal components from working underwater. Keep in mind that if you're talking, you're not holding your breath.

 The only real guidance we have on fireballs underwater is the Jeremy Crawford tweet Memnosyne linked above. and the one I've quoted below:
"Nothing in the rules causes a fireball to vaporize water. Magic ≠ physics. DMs may apply whatever magical/scientific logic they like"

An actual book rule from page 198 of the PHB "Creatures and objects that are fully immersed in water have resistance to fire damage."

A DM and player may also wish to consider page 204 of the PHB "To target something, you must have a clear path to it." for spells that require a clear path.  Its completely up to the DM where they put water in regards to a "clear path".  Even visibility might be an issue if the water is murky or reduces the range of visibility.  Air and transparent gasses are obviously no barrier to spells but a pane of transparent glass would present a barrier while opaque gasses and solids would also block visibility.  The best guidance I'm aware of is the Wall of Water spell despite it magical in nature: "Any ranged weapon attack that enters the wall’s space has disadvantage on the attack roll, and fire damage is halved if the fire effect passes through the wall to reach its target. Spells that deal cold damage that pass through the wall cause the area of the wall they pass through to freeze solid." The first thing to notice is that only ranged WEAPON attacks have disadvantage and a fire effect even passing through 1 foot of water then into air would halve damage even if the end target isn't submerged.  Regardless, as far as spells go, the suggestion is that passing through water wouldn't cause the spell any issues in hitting a target unless it was part of a ranged weapon attack. EDIT - Just realised that while fireball was given as an example, the "wall of water" text suggests ranged ice spells or effects might pass through but leave a solid wall of ice behind them.

Some fire spells set a target on fire and give guidance around how the fire can be put out, such as a Paladin's "Searing Smite".  If mundane means can put the fire out I see no reason it wouldn't be put out immediately after causing any initial damage. Things like the Fiery Shackles summoned by the Rune Knight's invocation of the Fire Rune likely wouldn't go out underwater, and although the "Create Bonfire" cantrip probably couldn't ignite anything, there's nothing saying it can be put out by mundane means while the caster maintains concentration.

If you rule that spells can't be cast underwater because of the line of effect blocking, players will just never have their characters go underwater unless forced to, and in that situation they will just resent the GM.

A scene underwater is cool and atmospheric (or not, if you can't breathe water :-) and I'd hate to miss out on the chance to set games there.

Also, if you can throw a javelin underwater you really should be able to shoot a spell underwater.

There is a bit of a logical disconnect that you can't stand outside a house and cast a fireball into a room through a closed window, but you can stand on the shore and cast a fireball at a point 20 feet underwater. I think it comes down to a practical matter, as Greenstone said. You have to do SOMETHING about spellcasting underwater, or else underwater just becomes a place nobody wants to go. Also, you can say the former is a solid obstruction while the latter is not. Basically, you just can't do one, and you can do the other, so it's up to your DM to come up for an explanation why.