The Pinn continues on to Pield Heath and Cowley, passing under the Grand Union canal before joining the Frays River, an anabranch of the Colne, at Yiewsley.

[2] During the Second World War only, the Pinn was dammed near Pinner High Street for water for putting out fires from air raids.

All local sewerage runs to the distant Mogden Sewage Treatment Works discharging its treated waters to the Tideway.

This spares the Pinn from the incident nitrogen, bleach (ammonia) and other chemical biohazards which many of its catchment homes and business use and/or discharge.

Worn tyre and motor oil run-off is from some roadside drains at biohazardous levels, particularly below the A40 road which is a trunk route of six lanes at this point (this becomes the M40 motorway to the west) – about 0.62 miles (1 km) of this slopes down to the river.