Wikisimpsons - The Simpsons Wiki
Local legend has it that General Sherman is "a hundred years if he's a day" and weighs upwards of five hundred pounds. He resides in Catfish Lake where he competes with wives for their husbands' time, as the location is popular for couples' retreats as well as fishing. A photo of General Sherman is on display in the local service station, where the shopkeeper tells the legend of the fish to the store's customers.
Homer caught General Sherman by accident. He saw a fishing pole that another fisherman left behind, and picked up to give it back to him. At that moment, General Sherman bit on the hook, yanking Homer off of the pier and into a boat, and then dragging the boat (with Homer) out onto the lake. After a lengthy struggle, Homer managed to haul General Sherman into his boat and knock him unconscious with an oar. However, he then saw that Marge was upset with him for spending time fishing instead of with her, especially because they were attending a marriage counseling retreat at the time.
After Homer realized he had to choose between the fish and his marriage to Marge, he decided to let General Sherman go. He later became part of the local legend about the fish, as told by Sneed: "Well, one fella came close [to catching General Sherman]. Went by the name of Homer. Seven feet tall he was, with arms like tree trunks. His eyes were like steel, cold, hard. Had a shock of hair, red like the fires of Hell ..."
 Behind the Laughter