Adopted 20 July 1976 on 82E/NW; an established local name according to April 1975 news release from BC Parks.

Source: BC place name cards, or correspondence to/from BC's Chief Geographer or BC Geographical Names Office

Longtime Kelowna resident J.H. Ivens advised in September 1991 that "Ogopogo" is actually the preferred local name, however Peachland Historical Society, BC Parks and municipal offices all state that "Rattlesnake" is indeed the well-established local name (file K.1.55). "Early settlers and residents before the mid-1950s simply called it "The Island". Sometime later the name "Sunset Island" was used by some area residents but as time progressed the use of Ogopogo and Rattlesnake come into more frequent and common use. During the past two decades, use of Rattlesnake Island has dominated, and is used by residents and the media almost exclusively to any other name." (August 2005 letter from Peachland Historical Society, file K.1.55)

Source: BC place name cards, or correspondence to/from BC's Chief Geographer or BC Geographical Names Office

Likely a reference to the Rattlesnake Grass (Glyceria canadensis) that grows here.

Source: BC place name cards, or correspondence to/from BC's Chief Geographer or BC Geographical Names Office

"As early as the 1700s, the Okanagan Indians knew of a water beast living in the lake. They called the creature N'ha-a-itk, meaning "snake of the water," and their Native superstitions demanded certain traditions before entering N'ha-a-ith's domain. One of the traditions was the ritual sacrifice of a small animal as a peace offering before crossing the lake. Tying their horses behind their canoes, they would paddle out to where they believed the serpent lived in a cave beneath the water---known as Squally Point---and make their offering, thus insuring that their horses would not be dragged under and drowned by the monster.
In 1890, Captain Thomas Shorts was steaming on the lake when he saw a finned creature about sixteen feet long with a head like that of a ram. The creature promptly disappeared when he turned his ship in its direction, and virtually no one believed him when he reported it. But other reports soon followed at [the rate of] two or three a year, and people began to examine the lake in more careful detail. The local population fervently believed in the creature's existence. They called it Ogopogo and named the island, Ogopogo Island. In the early part of the 1900's it was also called "The Island".
In 1951 it was purchased by Peter Spackman, who tried to have the name Sunset Island adopted, but it had, at that time, been given the moniker of Rattlesnake Island because of the grass that covers it. Many locals still called it Ogopogo Island but at the request of the Kelowna Chamber of Commerce in the 1950's the name of Rattlesnake Island was confirmed.
The island changed hands several times until Mohammed Eddy Haymour bought it in the early 1970's and then got into a conflict with W A C Bennett and the BC Provincial Government that ended as a hostage situation in the Canadian Embassy in Lebanon. It is story that is fascinating to read and it is now a part of the history of Peachland. "From Nut House to Castle" is the title of the book. As a result of the settlement of the Haymour case the island was returned to the BC Provincial Government." (September 2006 information provided by Michael Henderson, Peachland.)

Source: included with note