Octorox said:The 2D Clone Wars shows a lightsaber actually boiling the water around it underwater but again that isn't canon.
If I'm not mistaken, that lightsaber was made special to be able to operate underwater. Isn't there a cut scene from TPM where Qui-Gon berates Obi-Wan for getting his lightsaber wet, causing it to "short out"? That's the reason he was running from the STAP.