Which North American ancestor is largely credited with providing the backbone for the Flat-Coat's retrieving drive and water affinity?

Answer

St. John's water dog

Stock imported from North America, specifically the now-extinct St. John's water dog, is generally attributed as the foundation for the breed's retrieving ability and connection to water work.

Which North American ancestor is largely credited with providing the backbone for the Flat-Coat's retrieving drive and water affinity?
Dogbreedlineagecoatretriever