Use a long sword with thunder attribute and stand in front of it and to the right and attack its head when it sprays water from its mouth. Standing on the left side leaves you vulnerable to its powerful hip-check attack. And bring sonic bombs to force it out of the water. Also bring screamers and gun powder to make more sonic bombs. And never put yourself between the monster and a corner, if it knocks you down once you will most likely not be able to dodge its next attack.