The upper reaches of the River Kennet start with the winterbournes west and north of Marlborough, flowing past Avebury and Silbury Hill during the winter and drying naturally in the summer.
The Swallowhead Springs, opposite Silbury Hill are thought of as the start of the River Kennet. The river usually flows year round from Fyflield downstream to the market town of Marlborough, but in exceptionally dry years such as the 2011/12 drought the entire river upstream from Marlborough has been known to dry up.
Anecdotal evidence suggests that the upper reaches of the River Kennet dry more frequently since water abstraction began, and modelling by Action for the River Kennet (ARK) shows that the river dries more frequently as a result of water abstraction. The Environment Agency are currently reviewing this evidence.
The water body fails to meet Good Ecological status. During 2012/13 drought the upper Kennet dried up completely and many fish died. To help fish populations to recover, the main barriers to fish migration at Mildenhall (Durnsford Mill), Marlborough (Town Mill and Coopers Meadow) and Manton (Preshute House Weir) have been removed or modified by projects run by Action for the River Kennet.
In 2015 modifications to the Marlborough College Lakes and associated structures were identified as an important potential improvement which would benefit river water quality, fish migration and channel profile and dynamics. The project was reviewed by the Kennet Catchment Partnership in April 2018 and remains a priority for the upper Kennet if funding can be found.
The River Og
The River Og flows into the Kennet just downstream of Marlborough. It is a small chalk stream with a healthy brown trout population.
The upper reaches of the Og are winterbournes, and in recent dry years the river has dried up so that only the last few hundred metres remain with any water at all.
Recent studies into the effect of water abstraction on the Og have proved that the abstraction regime needs to change to protect the river. As a result water abstraction from the Og borehole was reduced to zero from 2015 and an alternative water supply to Swindon has been completed by Thames Water.
There are opportunities to improve the habitat for wildlife, particularly on the lower Og, including channel modifications to restore natural channel profiles and dynamics. ARK completed a habitat restoration project on the lower reaches of the Og funded by the Catchment Restoration Fund.