Coordinates: 50°41′45″N 1°59′19″W / 50.69583°N 1.98861°W
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.
Poole Harbour has an area of approximately 36 km2 (14 sq mi). Other large natural harbours are France's 120 km2 (46 sq mi) Gulf of Morbihan, New Zealand's 947 km2 (366 sq mi) Kaipara Harbour and San Francisco Bay in California with a conservative estimate of 1,040 km2 (400 sq mi) covered.
In 1964 during harbour dredging, the waterlogged remains of a 2000-year-old Iron Age logboat were found off Brownsea Island. Dated at about 295 BC, the 10 metres (33 ft) Poole Logboat is one of the largest vessels of its type from British waters. The low freeboard would have limited its use to within Poole Harbour.
Poole was used by the Romans as an invasion port for the conquest of southern England, who established the settlement at Hamworthy, now the western half of Poole. A Roman Road ran north from Hamworthy to Badbury Rings, a Roman transport hub. At the time of the Norman Conquest, Poole was a small fishing village.