The One That Got Away

Two men, a father and son, were fishing on the Tulpehocken Creek, a tributary to the Schuylkill River. At first, it seemed as though the creek was empty, and there wasn't a bite. But then a large school of fish swam by. So the men cast their line in hope of catching one. They were lucky, and it seemed as though they struck gold. The fish seemed endless, and one after another the men reeled them in. But then the father hooked something. Something that felt too big to be a fish. He fought, and he fought, and even with the help of his son, they couldn't reel in the fish. So the father tells his son to go and get the knife out of the tackle box, so that they could cut the line. The son does so, and when he returns, all he can see is his father being helplessly dragged under the water. The last thing he hears from him is a scream of horror. True or false? Nobody knows...