[citation needed] After running a mile down its limestone valley, the Leach reaches Northleach, the first settlement to which it gives its name.

A section of the river is confined into mill race type stonework, close to the churchyard and runs behind houses marking the town boundary.

It is still little more than ditch-sized, and as such continues down the valley to the hamlet of Eastington running alongside a lane before passing through a culvert and away through grazing land.

The river runs behind Lodge Park, a National Trust property, and through Larkethill Wood, where it flows under another lane, before passing Kilkenny Farm.

The bourn section had been running continuously for long enough to have taken on the appearance of a river, with a scoured bed and water plants.)

Here it is crossed by a stone slab clapper bridge on a footpath close to a wide marshy area.

A few hundred yards (metres) later the Leach discharges from the northern bank into the Thames on the reach above Buscot Lock.

There are several components that are used to determine this, including biological status, which looks at the quantity and varieties of invertebrates, angiosperms and fish.