The Wantsum Channel is the name given to a now silted-up watercourse in the English county of Kent. From prehistory until the Middle Ages it separated the island of Thanet at the north eastern edge of Kent from the mainland.

The Channel was emptied into by the River Stour which but was a wide strait fed by the North Sea that was around 2 miles wide during the Roman period. The southern end of he channel fed into the sea at Richborough near Sandwich and the northern end at Reculver. Both sites were chosen by the Romans for forts which indicates the significance of the route. It was also commonly used by merchants travelling between London and the continent.

Deposition of shingle from the North Sea began closing the channel in the early medieval period and land reclamation by the local monasteries also contributed to reducing the channel to a stream. A dense bank of shingle had begun to appear during the Roman occupation at the southern end of the channel at Stonar , forcing the waters to meander and slow down, accelerating the silting process. By the sixteenth century it was no longer navigable but the River Stour continues to follow its course. During the eighteenth century, the silting then threatened the rich port of Sandwich and efforts were made to create sluices and channels to control the waters. These ultimately failed however and as a result Sandwich is now some distance from the sea.