Without looking at the source material...
I'd say the alignment should be Neutral, not Chaotic. The sea is an uncaring thing - that's neutrality - more than chaotic in the way the GOOs are.
You have way too much focus on DPS spells, when no other pact even has one. Warlock, by design, is not a nuking caster class, they do buffs CC and IK - and if there was a Pact that was meant to give them more of a nuking toolkit, it wouldnt be Water, it'd be Air. Water is the least nukey of the four elements. And you dont have to solely draw from the existing arcane spellbook...you can adapt enhancement skills too (eg Warchanter freeze)
Also you give them a L14 pact spell that they've already had since L10
Pact spells are not SLAs, and its not like there's even a bunch of good L4 Warlock spells where you'd want to free up a slot.
The first special ability is pretty weak - maybe give a Waterbreathing+Merfolks Blessing combo spell as one of the early spells instead. I might go with +5% dodge/dodge cap as the first ability, a la Ocean Stance. Second one - summons, blech. Make it a no-save freeze.
I also always kinda thought of a Water pact as the best place to put a bit of self-healing for Warlock - Water Domain is linked to Positive SP for Clerics, e.g. Maybe one of their spells could be Vigor, which would play nicely with Feigned Life (temp HP + regen, like a mini-Cocoon)