The Harbour of Poole lies a few miles to the West of Bournemouth. It has an area approximately of 10,000 acres, but there is only a very narrow passage between its waters and the open sea. The width of this bottle-neck entrance is about 250 yards. The last published Admiralty chart gives the rate of the incoming tide through this narrow entrance at 3¼ knots, and of the outgoing tide at 4 knots. The local opinion is that these official rates err on the moderate side. The rapid ebb and flow of the tides has an influence in the bacteriology of the oysters within the harbour.