There is one main dredged channel through the harbour, from the mouth to Holes Bay in Poole, where cross-Channel ferries and cargo ships dock. The oldest known use of the harbour as a harbour for boats is 295 BC. A 10 metre log boat has been found preserved in the mud off Brownsea Island which has been dated as that age. Poole was used by the Romans as an invasion port for the conquest of southern England. At the time of the Norman Conquest Poole was a small fishing village. The port grew and in 1433 Poole was made Dorset's Port of the Staple, and was used to export wool. Medieval Poole had trading links from the Baltics to Italy. In the 17th century the town began trading with North America, in particular Newfoundland, and the town became very wealthy. In the 18th century Poole was the principal British port trading with North America. At the start of the 19th century 90% of Poole's population's employment was directly dependent on the harbour, but this dropped to just 20% during the century as the railways reached the town, and deep hulled boats moved up the coast to Southampton, which had a deeper harbour and is closer to London. With regular dredging of a channel through the harbour it has become an important harbour again.
Ecology & Nature Conservation
Much of the north side of the harbour is a built up area, part of Poole, and the conurbation which continues 10 miles eastwards along the coast. The west and south sides of the harbour and part of the Purbeck Heritage Coast and are important wildlife havens, as are the 5 large islands in the harbour which are some of the few homes to Red Squirrels in south England. The harbour is an area of international importance for wildlife conservation and borders 3 National Nature Reserves, including the internationally important Studland and Godlingston Heath NNR, and a number of local and non-statiatory nature reserves run by organisations such as the National Trust and RSPB. The mouth of the harbour is partially blocked by Sandbanks, a spit on the north, which is largely built up, and part of Poole, and by Studland to the south, which is another important wildlife area. Four rivers drain into Poole harbour, the largest being the River Frome, which flows from the west through Dorchester and Wareham. The harbour is very shallow in places and has extensive mud flat and salt marsh habitats, as well muddy shores, sandy shores and seagrass meadows. The area is an extremely popular recreation and tourism area, and local authorities and organisations have to carefully manage the tourism to prevent damage to the important habitats.