Hallsmead Ait is an island in the River Thames

River Thames

The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

 in Berkshire

Berkshire

Berkshire is a historic county in the South of England. It is also often referred to as the Royal County of Berkshire because of the presence of the royal residence of Windsor Castle in the county; this usage, which dates to the 19th century at least, was recognised by the Queen in 1957, and...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. It is on the reach above Shiplake Lock

Shiplake Lock

Shiplake Lock is a lock and weir situated on the River Thames in England near the village of Shiplake, Oxfordshire. It is just above the points where the River Loddon joins the Thames and Shiplake Railway Bridge crosses the river...

 near Lower Shiplake.

The island is large and triangular shaped, forming a pair with The Lynch, a similar shaped island. It is uninhabited and covered with a wide variety of trees. Although it is positioned towards the Oxfordshire

Oxfordshire

Oxfordshire is a county in the South East region of England, bordering on Warwickshire and Northamptonshire , Buckinghamshire , Berkshire , Wiltshire and Gloucestershire ....

 bank of the river, it is actually in Berkshire.

Berry Brook

Berry Brook

The Berry Brook is a stream close to Sonning Eye in the flood plain of the River Thames, in southern Oxfordshire, England.The stream flows northeast from close to the Redgrave-Pinsent Rowing Lake, parallel with the A4155 Henley Road ourt of Caversham, Reading towards Henley-on-Thames. It flows...

 starts close to the Redgrave-Pinsent Rowing Lake to the southwest, running northeast through the Thames floodplain, before joining the river at Hallsmead Ait.