Bishop, Michael. "And the Marlin Spoke"
Divergence: c 1500 CE
What if: North American colonization followed a slightly different path.
Summary: A farmer from a different Oklahoma makes a pilgrimage to the Gulf Coast of New Castile, where a cult of sea worship has sprung up.
Published: In The Magazine of Fantasy and Science Fiction, October 1983; and Close Encounters With the Deity, Peachtree 1986 (0931948967, 0934601070).