Eastney put-in (Portsmouth)

Langstone Harbour is a near-enclosed tidal basin of about 5,000 acres within nearly 15 miles of shoreline, of which almost 70% dries at low water. At high water it opens into a broad sheet reaching several miles north; as the tide falls it collapses into scoured channels, Langstone Channel to the north-east and Broom Channel to the north, threading between wide banks of drying sand and mud. The Run, the harbour's narrow entrance channel between Eastney Point and Gunner Point, reaches charted depths of 13 metres where the tide runs at its strongest.

The harbour holds around 600 moorings, with those on the west side of the Run belonging to the private Eastney Cruising Association. Eastney Lake forms the dredged approach channel to Southsea Marina, just north-west of the launch. Since 2022 the harbour board and Portsmouth City Council have cleared most of the abandoned vessels that once lined the Eastney foreshore, removing over 120 tonnes of degrading fibreglass, 20 tonnes of wood and 14 tonnes of metal, and reducing the number left from around 120 to fewer than ten.

The most conspicuous structure on the water is a concrete Mulberry Harbour caisson in the main channel, a D-Day-era unit that developed a fault before it could be deployed and was left in the harbour, where it later broke its back and remains charted there, with two visitor mooring buoys close by. On the Eastney shore, Portsmouth's RNLI lifeboat station has looked out over the harbour since 1965.