The name "Swale" is Old English in origin, and is believed to mean "swirling, rushing river", or "rushing water".[12]
Peri-glacial period
At these times the Swale was a gully from what had been a sea channel in very warm periods. Namely before the Strait of Dover had swept away so much swampy land, accentuated by sea levels being lower, even to beyond the end of the ice age, i.e. in the mid seventh millennium BC, the coasts of Essex and Kent stretched much further into the North Sea. Sheppey formed part of mainland Britain. The Swale was a valley opening eastwards. As sea-levels rose again, water occupied its whole length. It and the very mouth of the Medway divide the Isle of Sheppey from the mainland.
Roman Warm Period
When the Romans arrived in Britain, the Swale was much wider, with one part of the Isle of Sheppey — now called the Isle of Harty or Harty — a separate island.
Former ferries
Two c. 1600 to 1900 public ferries crossed the Swale. One operated between Oare and Harty, and the other between Murston (near Sittingbourne) and Elmley (another former hamlet and essentially attached islet). Harty is no longer separate but the marshlands gradually encroaching delineate it.
Dredging and channel traffic
The channel needs constant dredging for busy recreational and light vessel use.
^Ekwall, Eilert (1960), The Concise Oxford Dictionary of English Place-Names (4th ed.), Oxford: OUP, p. 455, ISBN978-0-19-869103-7. Mills, A. D. (1998), A Dictionary of English Place-Names (2nd ed.), Oxford: OUP, p. 335. While Ekwall takes the origin of this name to be identical with that of the Yorkshire river, Mills says it is "probably identical".
^"SSSI The Swale"(PDF). www.sssi.naturalengland.org.uk. 1968. Retrieved 12 November 2013.