Catfish in the Cradle by Wile E. Young
Grady Pope has hit bottom; his alligator hunting business is failing and his daughter has abandoned him. Nearly giving up, his life is turned upside down when she reappears and dies giving birth to a son. Grady takes in his erstwhile grandson, vowing to raise him. He soon notices that strange events occur around the child, culminating in the revelation that he isn't entirely human. The ancient forces who dwell in the river want their kin back and Grady Pope must decide whether blood does run thicker than water.