You can destroy 2 other monsters in your hand and/or face-up on your field, including a WATER monster, and if you do, Special Summon this card, and if you do that, you can banish up to 2 Spell/Trap Cards from your opponent's field and/or Graveyard, if both the destroyed monsters were WATER.

https://yugipedia.com/wiki/Problem-Solving_Card_Text#Conjunctives

In "Do A, and if you do, do B", both A and B happen simultaneously. A is required for B, but NOT vice-versa: if A does not happen, then stop; even if B cannot happen, you still do A.

If "destroy 2 other monsters in your hand and/or face-up on your field, including a WATER monster" did not happen, the rest of that effect does not resolve.