The river can rise, in a wet year, not far below Dudswell, about two miles north-west of Berkhamsted. But in past years, before the Three Valleys Water extraction point at New Ground was installed, it would have risen above Dudswell. The river is a typical chalk stream rising from springs dependent on the groundwater level in the chalk strata. Years ago it would have carried a good volume of water, sufficient at least to power two watermills in Berkhamsted, and another further downstream near Bourne End (two miles west of Hemel Hempstead).
Further competition for water is provided by the Grand Union Canal constructed in the early 19th century. This is primarily fed from reservoirs above Tring, but in a dry year additional water is pumped into the canal from the groundwater along its route, which has an immediate effect on the groundwater level supplying the river.
The river runs close to the canal throughout its length, mostly at a lower level. It suffers a loss of identity where it is diverted into the canal for about 200 yards in Berkhamsted before it exits at Bank Mill. It thereafter maintains some semblance of a river until it arrives at Winkwell not far below Bourne End. After a mile it emerges again as a river for about half a mile before joining the River Gade at Two Waters, Hemel Hempstead.
There are no fish in the river, but it serves as a useful feeding ground for ducks when there are no visitors to throw them bread.
Unless otherwise stated the photographs were taken in 1994. They follow the river from its source to Winkwell.
For more information about chalk streams: