7

As seen in Harry Potter and the Goblet of Fire, during the Second Task, we see Harry casting an underwater spell, but it has a different effect than usual.

"Relashio!" Harry shouted, except that no sound came out... a large bubble issued from his mouth, and his wand, instead of sending sparks at the grindylows, pelted them with what seemed to be a jet of boiling water, for where it struck them, angry red patches appeared on their green skin.

Harry Potter and the Goblet of Fire, Chapter Twenty-Six - The Second Task

Here, it seems that there is a problem with wording the spell, which is what causes a change in the effect. However, nonverbal spells don't need you to speak underwater. Does this mean that nonverbal spells would have the same effect underwater as verbal spells, or that it would have the same effect as above the water?

  • 1
    I'd image yes, with the obvious exception that the spell might react with the water after it leaves the wand. i.e. fire spells will be more akin to steam spells, any spells that would activate instantly upon hitting an non-air object would probably just immediately discharge in the water. a spell to charm an object might just charm the river etc.. – Ummdustry Feb 18 '18 at 18:39
5

They seem to work as they do above water.

The only other underwater sequence in the books occurs in Deathly Hallows. Ron cuts the locket horcrux off Harry.

All he could do was raise a shaking hand to his throat and feel the place where the locket had cut tightly into his flesh. It was gone: someone had cut him free...There before him stood Ron, fully dressed but drenched to the skin, his hair plastered to his face, the sword of Gryffindor in one hand and the Horcrux dangling from its broken chain in the other.
(Deathly Hallows, Chapter 19, The Silver Doe).

Given that he was in a life-and-death situation it seems inevitable that Ron used magic to cut Harry free. A Severing Charm would have done the trick.

We don't see Ron perform the spell so can't definitively confirm that he cast it non-verbally. However, the example of Harry and the Grindelows would seem in indicate to me that verbal magic doesn't work underwater. The nature of the spell Harry casts is fundamentally changed by the water. Water alters magic. This does seem to be partly to do with the difficulties of underwater pronunciation. If he tried performing Diffindo verbally then Ron would probably have blown a lot of bubbles as he was unable to speak the necessary incantation. The spell would have done something, as Harry's did, but any magic would be volatile, unpredictable and most likely unsuccessful.

Yet Ron's spell seems to have worked. The results speak for themselves. Either Ron cast a verbal spell which worked as a fluke or he cast it non-verbally.

I think it's much more likely that he used non-verbal magic. These spells were required of sixth-year Hogwarts students so Ron would've had the necessary knowledge.

Non-verbal spells were now expected, not only in Defence Against the Dark Arts, but in Charms and Transfiguration too.
(Half-Blood Prince, Chapter 11, Hermione's Helping Hand).

Apart from anything else, it's much easier to cast a non-verbal spell when you're underwater and the alternative is blowing bubbles. And, as I said, Ron was in a life-and-death situation. It's much more likely that he would cast non-verbally since he had the ability to.

3

It’s unclear, only one other spell was cast submerged in water.

The only spell (other than the one mentioned in the question) that was ever cast while the one casting it was submerged in water was when Dumbledore encased the Dark Lord in a bubble of water and then he escaped.

“At the same moment, Dumbledore brandished his wand in one long, fluid movement – the snake, which had been an instant from sinking its fangs into him, flew high into the air and vanished in a wisp of dark smoke; and the water in the pool rose up and covered Voldemort like a cocoon of molten glass.

For a few seconds Voldemort was visible only as a dark, rippling, faceless figure, shimmering and indistinct upon the plinth, clearly struggling to throw off the suffocating mass –

Then he was gone and the water fell with a crash back into its pool, slopping wildly over the sides, drenching the polished floor.”
- Harry Potter and the Order of the Phoenix, Chapter 36 (The Only One he Ever Feared)

We don’t know what spell the Dark Lord was using, so we don’t know if the effect would have been the same in the bubble of water or not - but it did break him free of it.

However (unless magic counters physics) some logically might change.

While it’s unclear what most spells might do if cast underwater, there are certain spells whose effects seem likely to change if cast underwater. Certain effects may not work underwater, and in addition, water may provide somewhat of a physical barrier against spells.

For example, Incendio shoots fire, which would likely not work as well underwater. Flagrate, Fiendfyre, and similar spells also might not work since they’re fire-based and the water could extinguish the fire. Similarly, spells that shoot off sparks might not work. Other spells that might not work are the ones that conjure land-based creatures like Avis and Serpensortia, since the creatures would likely drown and not be of much use.

  • I think he probably just Aparated (and so didn't cast any spell). – The Dark Lord Feb 18 '18 at 20:57
  • @TheDarkLord That seems likely as well, thanks! :) – Bellatrix Feb 18 '18 at 21:00
  • But as we see, Relashio (a spell that shoots sparks) shot boiling water instead. I think the same applies for spells such as Flagrante, though Incendio might be a different story. – MasterBob Feb 19 '18 at 2:16

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