The River Mimram in Hertfordshire is one of a number of tributaries of the Upper Lea. Its historic source is to the north of the village of Whitwell. From here it flows south, passing the villages of Codicote, Welwyn, Digswell, Tewin and Hertingfordbury, before joining the River Lea in Hertford. The river still supports a commercial watercress industry and there are several historic mills dotted along its length.
The main urban areas near to the Mimram are the towns of Welwyn, Welwyn Garden City and Hertford. Despite the predominantly rural nature of the river itself, a large population exists in the surrounding area. Water is abstracted at Fulling Mill and Digswell pumping stations to supply the surrounding towns and villages although this will cease in 2018 and 2020 respectively. This high level of abstraction has adversely affected the river for many decades.
This over-abstraction means that water levels in the river are significantly lower than they should be. This has adversely affected the characteristics of the river itself, and the health of the wildlife that depends on it. In addition, the river faces the problems of invasive species, pollution and physical modifications such as weirs.
Despite these problems, the Mimram remains one of Hertfordshire’s finest chalk streams. It is a noted fly fishing river, and is one of the few rivers in Hertfordshire that still supports populations of water vole. Birds such as green sandpiper, little egret and kingfisher are regular visitors to the river, and otters have been known to make passing visits.
The Mimram Valley is very rural, and consists mainly of farmland and privately owned estates. However, there is good public access at Singler’s Marsh near Welwyn, Tewin Bury Farm and at Panshanger Park, and the river remains beloved by the local community.