Sea snakes are not at all aggressive, and therefore rarely a threat.

 

There was a documentary a while ago about Aussie (?) divers collecting sea snakes to obtain their venom to use as anti-venom for the very rare bites.  They (obviously) sought out an area with a multitude of sea snakes (banded sea snakes IIRC) - and the snakes were being knocked about by the divers' fins, but never attacked.

 

As a diver myself, I've seen many sea snakes - and never felt any fear of being close to them whilst diving.

 

Having said this, if they're sick enough to be so close to the beach - I'd give them a very wide berth.

pretty easy to avoid one of these. i would be much more worried about a box jellyfish that ARE in the area and i believe have killed at least one soul in phuket area

once at low tide at a bali club med beach was walking my board out to deeper water and as i about to take next step saw a sea snake in strike stance. my toes are not too big for it. i froze and very slowly backed that foot away. returned to beack.  many cubby holes filled with sea snakes at the very popular beach at club med.

 

at uluwatu when the tide is too low for non life or death surf a tide pool is filled with them and nice to watch.

 

thai cobra antivenom can help if sea snake antivenom is not imediately available

https://www.researchgate.net/publication/11852783_Effectiveness_of_Thai_cobra_Naja_kaouthia_antivenom_against_sea_snake_Lapemis_hardwickii_venom_Verification_by_affinity_purified_FAB'2_fragments

I took some time to check the species and the one washed up on Phuket in my photo is a yellow bellied sea snake.  At first I thought they didn't look yellow enough, but the tail is the exact same and so is the colouration, just a bit more brown than yellow, a possible regional variation?  they're also highly venomous, like the kraits.  so definitely a snake, and not an eel.