Cookham Lock is a lock with weirs situated on the River Thames near Cookham, Berkshire. The lock is set in a lock cut which is one of four streams here and it is surrounded by woods. Next to the lock island is Formosa Island, the largest on the non-tidal Thames.
There are several weirs here. Hedsor weir was placed across the old navigation channel in 1837, seven years after the lock was opened. There is a lower weir, and Odney weir is on the channel next to Formosa Island.
The navigation route was formerly down Hedsor Water and the only weir was associated with the mill. After the building of Marlow Lock in 1773 there were problems with shallow water upstream, and the earliest suggestions were for a stop at Cookham to hold the water back. In 1794 it was considered one of the most dangerous parts on the river, mainly on account of chalk boulders falling into the Thames. However nothing happened until 1829 when a cut and lock were agreed upon, the cut going through the northernmost island called The Sashes. Part of the cut was formed from an existing Sashes Stream, and an Ait was removed at the lower end of the cut. The lock opened in 1830, but no weir was built at this time.
In 1832 Lord Boston of Hedsor House claimed compensation for loss of towpath rights along Hedsor Water which he was granted. In 1837 a weir was found necessary and built, leading to further litigation from Lord Boston for loss of trade to the wharf he owned there. This time the only compensation he received was the building of a flash lock in the weir. This was removed when the lock was rebuilt in 1869, as Lord Boston had built eel bucks in the stream in the meantime.
The lock was rebuilt in 1957.
There is a road from Cookham to Formosa Island and the lock.
After the streams rejoin above the lock, the river is crossed by Cookham Bridge. Along the reach on the Buckinghamshire bank is Bourne End where the River Wye joins the Thames. Bourne End Railway Bridge, which includes a footbridge, crosses the river here. Along the Berkshire bank there are water meadows. There are navigation transit markers just downstream of Bourne End Railway Bridge, to allow river users to check their speed.
Further upstream towards the Berkshire bank are the Gibraltar Islands which lie in front of Quarry Wood. There are then steep hills overhanging the river at Cookham Dean where the house called "The Mount", where Kenneth Graham lived as a child is situated. He based much of his book on this part of the Thames which is described as Wind in the Willows country.
As the ground levels, the Marlow By-pass Bridge crosses the river a little way downstream of Marlow Lock.