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 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: 48cm), with one main dredged channel through the harbour, from the mouth to Holes Bay.
Poole Harbour is one of several which lay claim to the title of the largest or second largest natural harbour in the world (Including Cork Harbour in Ireland and Halifax Harbour in Canada)