"Navvy"

I've heard that the word "Navvy" meaning manual worker, comes from Navigator - the men who worked on the North American Railroad. I have a feeling that the word is older than that. Can any of you knowledgeable ones enlighten me please?

Doris

The Oxford English Dictionary says it comes from one sense of "navigator," defined as "a labourer employed in the work of excavating and constructing a canal, or, in later use, in any similar kind of earthwork." Earliest citation for this sense of "navigator" is dated 1775; for "navvy," 1832.

And "navigator" with that meaning comes from "navigation," which once meant "a canal or other artificial waterway. Now dial[ectal]" (OED).