intertwined with the Wey and Godalming Navigations. The of the navigations' towpath is open to pedestrians. The river joins the Thames at a cascading channel off its Navigation Canal (above Thames Lock) between Hamm Court and Whittet's Ait and a weir-fed navigation east of the ait facing the main weir stream of Shepperton Lock. Tributaries The River Ock joins at Godalming, Cranleigh Waters and the River Tillingbourne at Shalford and the Hoe Stream at Woking. History The river has long been used as a source of power for mills, and many are recorded in the Domesday Book. Between the 17th and 19th centuries there were over 40 mills on the river and more on its tributaries. At various times they have been used for grinding grain, fulling wool, rolling oats, crushing cattle cake, leather dressing, paper production and gunpowder manufacture. Willey Mill, at Farnham, was still in use in 1953. Headley Mill is still in commercial operation. Guildford Town Mill, though no longer used for milling, still harnesses the power of the river to generate electricity. During the seventeenth century, the river was made navigable to Guildford and extended in the eighteenth century to Godalming. The Basingstoke Canal and Wey and Arun Junction Canal were later connected to the river. The navigable sections are now owned by the National Trust. Natural environment Wey Valley is a term for the narrowing basin of the River Wey before it empties into the River Thames. Much of the upper reaches of the river are within the Surrey Hills Area of Outstanding Natural Beauty. The river passes through a variety of habitats including heathland, woodland and watermeadow, resulting in a diversity of wildlife. There are Sites of Special Scientific Interest (SSSI) and Nature Reserves along the river. A broad basin of aquifers drain steeply to the river so, as with the Mole, in its natural state, much of the flood plains were prone to regular flooding. This has been greatly reduced by flood alleviation measures, upstream lakes such as Frensham Great Pond and, inadvertently, the Wey navigations. The lowest urban areas of Godalming, Byfleet and Weybridge saw extensive flooding in the exceptional winter storms of 2013–14. Water quality The Environment Agency measure water quality of the river systems in England. Each is given an overall ecological status, which may be one of five levels: high, good, moderate, poor and bad. There are several components