Waterblight Ganon is a formidable foe encountered multiple times. It wields a massive spear and can summon ice blocks. Phase 1: It attacks with wide spear swings and lunges. Dodge these and counter-attack. When it summons ice blocks, use Cryonis (L + X) to destroy them, which often exposes its weak-point gauge. Phase 2: At lower health, it will float and summon more ice. Use Revali's aerial attacks or Link's bow to hit it.
Mipha is an excellent choice for this fight due to her mobility and healing. Daruk's Protection can also block its attacks. When it charges its spear, use Stasis to interrupt. Its elemental weakness is fire, so if you have a character with fire attacks or a fire rod, use them. Rewards include Blight Ganon parts and high-level weapons.