The tour once crossed both Telegraph and Swinomish Sloughs linking the mainland with Fidalgo Island, where the route continues. Telegraph Slough is now filled and reclaimed. Swinomish Slough is now known as Swinomish Channel.

The island, separated from the mainland only by shallow sloughs, was named for Salvador Fidalgo, an explorer in one of the Spanish expeditions of 1790-1. A town called Fidalgo flourished briefly in this vicinity until the collapse of a railroad boom in 1892.

Swinomish Channel is a shallow, saltwater arm of Puget Sound, which extends north from Skagit Bay to the south end of Padilla Bay. Until 1954, when the present name was substituted, the accepted name was Swinomish Slough. The name is for the Swinomish Native American people, who live on the reservation to the west of the channel and are a branch of the Skagit people.