This post, at The Living Notebook gave me the title and the impetus to write on this subject here.
The line comes from Hemingway and TLN – I'm sorry, but the blog appears to be anonymous and I don't have the writer's name… – uses it to weave a connection between two approaches to writing.
We tend to either write while "fishing in the river," a line from a Nick Adams story in Hemingway's collection: Big, Two-Hearted River. Or we come around and finally "fish in the swamp."