Michael Rogers, 64, landed one of a handful of tagged fish Saturday, the Anchorage Daily News reported.
"I've been fishing this derby since it started pretty much, since I was a little kid. I've won quite a few prizes, but this is the first major one," Rogers told the Daily News in a telephone interview.
Rogers said things weren't going his way at first, but then he changed things up and started catching salmon.
When he returned to derby headquarters, Rogers said he was told one fish could be worth anywhere from $100 to $50,000.
"I had to sit in the derby office for a while and fill out paperwork, and finally they handed me an envelope," Rogers said. "All the women in there sat around me with and had pictures taken with me and then they said, 'OK, you can open it now.' And there was another envelope inside that one. So then I opened that one up and it says $50,000. It was quite a shock."
The Daily News said it was the second time in the derby's 57-year history that a $50,000 tagged fish was caught. The first one was caused in 2003.