Student or Learner
Hi, can I say
I like plunging in the sea
I like diving in the sea
'Plunging' is often transitive (He plunged the bucket into the pool) or metaphorical (The excited children plunged into the dressing-up trunk they'd found in the loft).
It would be wrong to say "the verb 'plunge' is not used to mean 'dive' - in the sense of 'throw oneself into water', but it's much less common than 'dive'. And in the context 'I like ...' diving is - in my experience - the only possibility (of the two!)
The other thing about 'dive' is that it can mean either 'enter the water head-first' or 'do a deep dive' or 'do a shallow dive from the surface of the water' ('duck-dive'). So 'I like diving' is ambiguous!
"plunge" can also be more graphic/dramatic:
'On the first day of his holiday, he dived into the hotel pool.'
'Regardless of his own safety, he plunged headlong into the raging torrent.'