I remember the first time I went fishing with my stepfather(I was around nine or so) and he told me this story of a friend of his who had supposedly seen a giant catfish in Millerton Lake.
The story goes that the man was fishing around the Friant Dam, when, while he was moving around, accidentally knocked off the boat motor. He was able to make it to shore using the trolling motor, but decided that he wanted to try to retrieve the motor as it was new and he had paid a lot for it.
The man rented some dive equipment and returned the next weekend. To lift his motor back to the surface, he took with him several large balloons that he would fill with a small auxiliary tank that would lift the motor back to the surface. After descending to the bottom, he began searching for his motor. After several minutes he came across something that he wouldn't have believed if he hadn't seen it for himself. Staring at him was an extremely large catfish. According to him the mouth was so big it could have easily have swallowed him. He estimated the length to be between 8-10' long. This was a quick estimate has he didn't stick around long enough to get a thorough look at it. Needless to say he got the hell out of there and never did retrieve his motor.
Now I don't know if this story is just another variant of the big fish that got away or something else, but I thought it was worth mentioning. I know back east, especially in the south large catfish have been known to be caught. Some even match the descriptions that I mentioned above. And catfish do have a fast growth rate, and they continue to grow all there life.
I wouldn't be surprised if there were several large catfish at the bottom of Millerton Lake near the dam hiding where no one will bother them. Their only company a forgotten motor boat engine that has long since rusted away.