take a toothpick and clean the fuzz out of your charge port. That might fix it. Seriously. Junk can get in there.

if its belt driven underneath, check the belt. ALso, make sure something inside isnt stopping the unit from turning i.e. a long knife or dish handle blocking the turning jet arm.

Most likely your battery or battery connections.

super precise diagonal pliers for fine electronics or circuit board work are also a good idea. If you can precisely bite the top rim of said screw perpendicular to the rim, and jus give it enough turn, she'll at least loosen. You should hear a little click when it breaks itself free. You all know what I mean.

Totally water submerged?

Once the unit is away from its power source, way away, take it outside in a ventillated area and pour isopropyl alcohol through the device, letting it displace the water as much as humanly possible. If its a camera try not to overdo it as to screw up the optics, If the optics are already contaminated, the alcohol thing might help but you still need to get the optics serviced.

for non-optical, keep the alcohol rinse/flush going a couple times and let the device either sit out and dry, blow a fan through it, or do the rice trick. The objective is to remove the bad ionization and water from the device. Alcohol dries quickly and mixes with the water. It should leave it very dry inside. If its salty salty salt water, your gonna get limited use of the device after this procedure and it would be advised to get all data out of the device asap (say if its a phone). The ocean salt water will have already done damage and is nearly impossible if not totally impossible to recover from fully