Upper River Thame


This is the upper section of the Thame, from its source on the Hertfordshire border near Marsworth to Thame on the Oxfordshire border. Its catchment isn’t large, but the river is fed by a number of significant tributaries, as well as the Aylesbury sewage treatment works (STW) which, at times, can be responsible for over 50% of the water as the river leaves Aylesbury. (Do not be alarmed by this as Thames Water make every effort to ensure that the water leaving the STW is of a very high standard.)

Thame River summer near mill

River Thame at Cuddington Bridge

The Thame is formed from two streams that run through agricultural land from near Marsworth and close to the Aylesbury arm of the Grand Union Canal. The land has only gentle undulations as the stream passes Rowsham and then turns south to Watermead Lake on the edge of Aylesbury. The Thame is joined by Hardwick Brook on the northwest corner of the town, after which it turns south, passing the STW and on to Eythrope, where Lord Rothschild lives. This is the start of a beautiful section of the river where the valley becomes more defined as it runs between water meadows at Nether Winchendon, Chearsley and Notley.

There is a large fish pass at Eythrope (accessed from Stone) and several of the farmers along the river, particularly Waddesdon Estates, Manor Farm Chearsley and Notley Farm, put significant resources and effort into their wildlife and the river.


The Valley at Cuddington, overlooking Winchendon. (doug-kennedy.com)

Thame River with tall reeds

The River Thame, upstream from Wichendon  (doug-kennedy.com)

There is a lot of reed growth along this section and river flows are very variable. In dry periods, much of the water comes from the Ayesbury STW, along with 6 other small plants attached to villages along the valley, and flows can be slow, making the performance of the STWs particularly critical. This is why the Trust has regular meetings with Thames Water to review the performance of sewage treatment. In wet weather, the Thame floods over an extensive area of water meadows, particularly around Winchendon and Chearsley.

Miraculously, although Cuddington Mill can be surrounded by floods, the water never encroaches the building.

The river passes some historic sites, such as the moat system at Chearsley and Notley Tythe Barn and Abbey, before skirting the Crendon industrial park and crossing the county border at Thame. By this time, the river has been fed by water from a number of good-sized brooks, so is wider and has a more regular flow, although in the winter the river floods across a wide area of water meadows to the west of the town.

Thame River at Chearsley

The Thame at Chearsley (doug-kennedy.com)

Cuddington Mill Stream 12-05-2016 10-13-33

At Cuddington Mill (doug-kennedy.com)

The Environment Agency Water Framework Directive classifications split this upper section of the Thame into two:

Thame to Aylesbury. This section is classified as “moderate”, based on multiple factors including fish, macrophytes, and invertebrates. Both dissolved oxygen and phosphates are classed as “poor”, with macrophytes being “moderate”. This is not surprising due to the large sewage treatment works and presence of agricultural land. Currently there is no data listed for fish, but following the restocking of the river that took place in 2014, chub, roach and dace of all sizes have been seen and anglers report some improvements. Surveys currently in progress will give us a better picture of the river’s health.

Roach in the Thame at Winchendon 2

Roach in the Thame near Winchendon (doug-kennedy.com)

It is not easy for fish to move along the river owing to a number of mills and other blockages, although there have been improvements at Eythrope and Cuddington Mill. There are no 2027 targets available at the moment.

Aylesbury to Marsworth. This section is classified as “poor”, which is an improvement from its 2009 “bad” status. According to the data, this section is only “poor” due to the macrophytes, with all other measurables being at least “good” or “high”, which may be surprising considering the slow flow and clogged status of the river channel. There are some gaps in the data here, and we would like to see more recent water quality analysis. This section is targeted to reach “good” status by 2027.

You can find out more about the classification of rivers in our catchment by using the Environment Agency’s Catchment Data Explorer.


Small Waters

The river isn’t the only water that we are concerned with. There are multiple small waters including ponds, ditches and steams. All of which are highlighted on the map below.upper-thame-small-waters


Eythrope Habitat Works

Eythrope Fencing

Waddesdon wetland creation

Arable Advice Project


We have a good amount of information on this section of river. Doug Kennedy, one of our key volunteers, has walked this section of the river and helped to build up an excellent picture of the river using his photographs (which can be viewed here).

Our summer intern, Ellen Robson, is also currently writing her dissertation project on the main River Thame. She surveyed 25 sites across August and we will be hearing what she learned at the end of this year. We hope that these surveys will help us to learn more about the biology of the upper parts of the river especially.

Our volunteers work hard to monitor the quality of the water across much of its length, and whilst the bird surveyors carry out monitoring once a month, we would love to increase the amount of data we receive, so take a look at how you can get involved here.

Other Groups

We are not aware of any groups that work specifically on this section of the River Thame, although there are angling groups who fish here. If you have information on groups who might be looking after the upper River Thame or would like to get involved in joining or starting a local group in your area, then please get in touch.


Winchendon. Credit: Jonathon Baines

Winchendon. Credit: Jonathon Baines

Eythrope Lake. Credit: Jonathon Baines

Eythrope Lake. Credit: Jonathon Baines