Penton Hook Lock is a lock on the River Thames in England situated on the northern "Middlesex" bank near Laleham, Surrey. The lock cuts across a large loop or hook in the river, creating Penton Hook Island There is a large marina (Penton Hook Marina)in the disused gravel pits connected to this loop. At over 266 ft (81.28 metres) it is the third longest lock on the river. There are two weirs, which were built some time after the lock. One weir links across to Penton Hook Island, and the other from the island across the old course of the river. The former weir has a wide footpath to the island, but the footpath across the other weir is closed.