The main tributary is the Tillingbourne, which rises on the western slopes of Leith Hill and flows westwards to join the Wey to the south of Guildford, between Shalford and Peasmarsh.

[2][3] The Wey north branch, sometimes referred to as the Alton Wey,[4] has its official nomenclature source in Alton in Hampshire; however is exceeded by length and, in wet weather, in flow by the nearby Caker Stream rising in dendritic drainage spanning fields of Upper Farringdon and Hartley Mauditt, passing Chawton between these places.

After the union in Alton the brook runs quite straight, east north-east through Upper Froyle and Bentley, turning southeast after Farnham's centre to Tilford.

A vestige of this is that the upper Blackwater valley proper, north of today's wind gap, is not lower than 226 feet (69 m) (Tongham Pool) and of very low gradient.

[6] Great erosion has occurred in the Wey down to Tilford, along the sinuous, multiple-anabranch Waverley Abbey stretch, through, what Blyth notes as, the "soft strata",[6] of that landscape.

The Wey South branch stems from two main westward brooks, one now followed by the Portsmouth Direct Line,[n 2] the other – with longer source brooks – following the Surrey/Sussex boundary,[n 3] which combine at a point, heading west, where the line first comes as close as 97 metres to the boundary – in the east end of a park, next to one of its three river footbridges.

These drain parallel, north, narrow vales between the northerly "fingers" or "ribs" of: The northern streams drain fingers of a single east–west ridge of Greensand, their common names, again from east to west, are: Of varying size, these are long, sandy hills south-east of the upper tip of the Devil's Punch Bowl: Gibbet Hill, Hindhead.

The south sources are specifically: a wood-surrounded neighbourhood, Kingsley Green (formerly Marsh) in Fernhurst;[9] Chase Farm marking the furthest point south in Surrey;[10] and upper fishponds at Wades Marsh marking the Fernhurst/Lurgashall boundary (both in West Sussex), next to the summit of Ridge Hill (which is the furthest source).

[11] The Wey drains and passes Haslemere's western suburbs then Liphook, Bramshott (including Passfield), Standford and Lindford, and the large parish of Frensham.

[5] From Tilford, the river runs through Elstead, Eashing, Godalming, Peasmarsh/Shalford, Guildford, Send, Old Woking, Pyrford, Byfleet, New Haw and forms the historically much more meandering border between Addlestone/Weybridge, today doing so most accurately between Hamm Court and Whittet's Ait respectively.

At various times they have been used for grinding grain, fulling wool, rolling oats, crushing cattle cake, leather dressing, paper production and gunpowder manufacture.