The Evenlode is the Cotswolds most Easterly river. It rises in the vicinity of Moreton in Marsh and flows South through Kingham and the Wychwoods after which it loops North East through Charlbury before being joined by its major tributary, the Glyme, just outside Blenheim Park. From there it flows South to the Thames at Cassington. The limestone here seems to have a limited capacity to hold water with the result that the Evenlode is liable to sudden and dramatic flooding following heavy rain at any time of the year.
The Evenlode’s major tributary is the Glyme which rises near Chipping Norton and then flows to Enstone, through Wooton and on to Woodstock, outside of which it joins the main river.
The major problems on the Evenlode and the Glyme are a massive infestation of signal crayfish and diverse agricultural pollution.
The Windrush rises to the North of Naunton and flows South East to the tourist Mecca of Bourton on the Water where its flow is swollen by the Dikler, which is itself joined by the Eye just outside the town. From Bourton it flows South to the village of Windrush where it is joined by the Sherborne Brook. It then swings East to run through Burford and on into Witney, where the stream splits into two and runs as two parallel rivers South to Standlake, after which the streams reunite and enter the Thames at Newbridge. As with so many Cotswolds rivers, the Windrush has been damaged over the years by a combination of dredging, abstraction and agricultural pollution. A major symptom of this is a lack of emerging fly life although the mayfly and the grannom are important exceptions to this. The mayfly hatch on the Windrush is one of the natural wonders of the Cotswolds. At its height, the roadside hedges appear from a distance to be giving off dense clouds of smoke, such are the numbers of dancing male spinners above them. The Windrush’s limestone aquifers hold more water than the Evenlode’s, but although not as volatile as that river, the Windrush will still flood after heavy rain. The Windrush has a particular problem with turbidity during the Summer months. On the plus side, it is one of two Cotswolds rivers to sustain a population of grayling.
The principle Windrush tributaries are the Dikler, the Eye and the Sherborne Brook. The Dikler rises above Upper Swell and flows south past Lower swell and the Slaughters before joining the Windrush below Bourton on the Water. The Eye’s source is not far from the Dikler’s and it runs down through the Slaughters to join the Dikler just north of Bourton on the Water. Grayling are present in the Dikler below Bourton and may be prevented from moving upstream by the gauging weir. Dippers are seen from time to time on the Dikler's upper reaches. The Sherborne Brook which enters the Windrush at Sherborne is, as its name suggests, a very small stream, but its water is of high quality. The Dikler suffers from abstraction close to its source at Upper Swell. This robs the whole length of the river of water and, in terms of environmental damage, is the worst possible site for a pumping station.
Tthe little River Leach rises in the vicinity of Northleach, before flowing South East through East Leach and Southrop and joining the Thames just below Lechlade. This is a small stream which usually runs crystal clear, even when swollen by rainfall. Water quality is generally good, although there is evidence of some decline below Lechlade.
The Coln rises near Andoversford and runs to Withington from whence it flows South East through Coln Rogers, Ablington, Bibury, Coln St Aldwyns and Fairford before joining the Thames just upstream of Lechlade. The Coln draws most of its water from the limestone aquifers, although it has been known to flood after very heavy winter rains. Like the Windrush, the Coln can suffer from turbidity during low flow periods. Above Fairford, ranunculus is abundant (to the point that weed cuts have to be organised) and fly life is equally abundant as a direct result of this. Below Fairford, aquatic vegetation is notable by its absence and hatches are mainly restricted to grannom and mayfly. Above Fairford there are good olive hatches from mid April through to the end of the season with sedges joining in after the mayfly. In addition to trout, grayling are present throughout most of the river, although there is evidence that their numbers are declining.
The biggest problem on the Coln is over abstraction with the upper reaches drying up during the drought year of 2011. Low flows also cause turbidity and a decline in upwing fly hatches. The lack of aquatic vegetation below Fairford is also a major concern.
This charming little Cotswold stream rises at Seven Springs (also touted by some as the true source of the Thames) and runs South through Colesbourne, North Cerney, Cirencester and South Cerney before joining the Thames near Cricklade. The Churn is another example of a mainly aquifer fed river, although the steep valley sides in the upper reaches mean that heavy rain can cause it to quickly rise, and equally quickly fall. Like all Cotswold Rivers it enjoys a good mayfly hatch and in well managed stretches there are good hatches of fly during the rest of the season. The Churn rises near the highest part of the Cotswolds, with the result that the water in its upper reaches tends to stay cold. Grayling are present in the lowest reaches of the Churn. However, the lower reaches of the Churn are severely over abstracted and dried up during 2011.