The 'River' Swale, or The Swale to gives its correct name, is the 13 mile channel that separates the Isle of Sheppey from the mainland of north Kent.
[The Swale is not a river, given that it is tidal at both ends and has no source.] 
The Swale's eastern end at Harty Ferry joins the River Thames estuary three miles west of Whitstable, while its western end flows into the River Medway at Sheerness.
It is tidal, with tides flooding from both ends and meeting about halfway off Milton creek and, together with its creeks of Faversham, Oare, Conyer and Milton, forms one of Kent's most attractive sailing areas.