My River Home Is Barred by a Wall of Man: Who Am I?

I have the body of a great serpent and the head of a fish. My domain is the mighty river that thunders over a smoking cliff, and my people are those who live along its banks. They built a great wall of concrete that holds back the water, a barrier that separates me from my beloved wife. The tremors they feel and the misfortunes they suffered while building it were but whispers of my wrath.