Catfish move up into creeks to spawn just like other fish do. Blues especially. It may be mother nature's way of insuring a concentrated food supply for all the baby fish. Lot's of eggs and lots of fry to feed on in a small area plus all the vegetation washed in by the spring rains. By summer's end most of the surviving spawn will have dropped back into the main lake.
Infidel and proud of it.
From Genesis: "And God promised men that good and obedient wives would be found in all corners of the earth."
Then He made the earth round...and He laughed and laughed and laughed!