Poole Harbour is the thing the town is built around, and understanding it explains almost everything else about the place: why the Old Town is where it is, why the beaches are where they are, and why half of Dorset learns to sail here.
Size and shape
At around 36 square kilometres at high water, the harbour is among the largest natural harbours in the world. It is also extremely shallow, mostly under two metres outside the dredged channels, which is why the water stays flat even in a strong wind and why it is so forgiving for anyone learning on it.
The entrance, between Sandbanks and Studland, is narrow, and an enormous volume of water moves through it on every tide. That makes the gap fast-flowing and no place to swim.
The islands
Brownsea Island is the largest and the only one open to the public, managed by the National Trust, with red squirrels, peacocks and a lagoon that draws birds in thousands. The smaller islands are private or managed for wildlife.
Wildlife and protection
The harbour is a Site of Special Scientific Interest and a RAMSAR wetland. In winter the mudflats fill with waders; ospreys pass through on migration. It matters, and it is fragile: see Respect, Protect, Enjoy.
Boats
Poole Harbour Commissioners manage navigation, moorings and commercial traffic. If you are arriving by sea or keeping a boat here, see marinas and chandlers. For getting out on the water without owning anything, see boat tours and watersports.