THE NEEDLES, ISLE OF WIGHT - Photo by Julian White 1 The Solent, or strait, was formed more than 7,000 years ago when the Isle of Wight separated from the mainland. 2 A recent theory is that the Solent may have been a lagoon with the River Frome in Dorset as its source, together with its tributaries the Rivers Avon, Test & Itchen. 3 The Solent River estuary gradually flooded at the end of the Ice Age. The chalk ridge between the Needles,