From Berkhamsted to Boxmoor, the river Bulbourne is inextricably linked with the Grand Union Canal. At the Old Mill public house, (formerly ‘Lower Mill’; the ‘Upper Mill’ was in central Berkhamsted) the river re-emerges from the canal, having been totally subsumed by it for some 200 metres. Occasionally surplus canal water is weired into the river, and at the third Bulbourne Mill (now the Watermill Motel at Bourne End) the river joins the canal and the waters weir down together to the river at its lower level.

At Chaulden the river joins the canal again, but crosses it to run then on its northern side as far as below Fishery Lane where it channels under the canal thereafter to flow through Boxmoor meadows. The chalk stream quality of this river is thus clearly compromised below Berkhamsted, although also road run-off problems are serious all through the urban areas. Artesian wells (eg at Sharpes Lane, for the old cress beds) and natural springs along the course of the river do help, but there is an obvious lack of typical chalk stream aquatic vegetation - and hence related fauna - for most of the river’s length, and water quality tests give ‘poor’ results.

Watercress production was once of great importance, with evidence of cleaner and more plentiful water. Numerous weir structures indicate the old beds, which even were present in central Berkhamsted, and many pools and fishing lakes now occur where the cress beds once thrived.