Waterblight Ganon telegraphs his attacks - mostly a thrust, a spear throw and if you get close enough, an attack that shakes the ground beneath him (browse the gallery above to see them all).
Our preference is that you keep your distance and rely on arrows for your primary attack. Waterblight Ganon's fighting style changes depending on how close (or far) you are from him. Breath of the Wild Waterblight Ganon part 1