Hi, welcome to the forum. The light itself is not sealed properly, hence the water in the unit, this is causing the gfi to trip. Take it apart and let it dry, inspect the gasket for dry rot or being worn out. The original problem was probably that the retaining screw wasn't tight enough and let water seep in, crank that puppy tight. When you put it back together, submerge it for a minute and check for bubbles, pull it back up and gently shake it to see if water has seeped in, if neither of these has happened, reinstall the light. If you experience any trouble with doing this, let me know and I'll help you as much as I can