13 foot ain't that big a deal, they got em all over the place. Size is a function of age, gators never stop growing, so you get the really big ones in the wildlife refuges where they are not disturbed. In populated areas, they are usually hauled off to the refuges when they get to be about 7 ft or so. Gators are also cannablisitc, they tend to keep their population in check by eating each other.

Bay City is near the huge Aransas National Wildlife Refuge (one of the most incredible places to visit in Texas, BTW) , I bet the critter migrated up from there. If you ever want to end it all by alligator, that's the place to go swimming.

I agree they are a nuisance in populated areas. They are not really all that dangerous to humans if they are not allowed to get large, but they eat cats and dogs for snacks, and sure do ruin a good jogging trail. I felt really bad for the elderly lady I ran into along a Brazos Bend State Park hiking trail who had just had her toy poodle swallowed, I was saddened by her loss. If you ever visit any South Texas parks, leave Fido in the car.