Poole Harbour is a large natural
harbour in Dorset, southern England, with the town of
Poole on its shores. The harbour is a drowned valley (
ria) formed at the end of the last
ice age and is the
estuary of several rivers, the largest being the
Frome. The harbour has a long history of human settlement stretching to pre-Roman times. The harbour is extremely shallow (average depth: 48 cm), with one main dredged channel through the harbour, from the mouth to Holes Bay.