Water Quality

Water Quality in the Thame

If we look at the data from the Water Framework Directive (WFD), the 2015 water quality data from the Environment Agency suggests that water quality across the different streams and brooks in the catchment are either “moderate” or “poor”. No areas of the catchment achieve “good” status currently . Factors influencing the water environment in the Thame catchment are likely to be urban and rural diffuse pollution, waste water discharges, road run-off, habitat/land management, modifications and invasive non-native species. It is important to note that there have been vast improvements over the years, but in order to achieve the most biodiverse river we must work hard to further improve our water quality.

The River Thame flows through a gentle, rolling English landscape from north of Aylesbury in Buckinghamshire, to join the River Thames at Dorchester on Thames. Much of the land that meets the river is agricultural, with some densely populated areas in Aylesbury and Thame. It is a combination of agricultural practices and waste water discharges that have the biggest impact on our river as a whole. Both of these issues are explained further on their own pages.

Thame dead fish

A large dead fish, one of many, on the River Thame in 2013.

Unfortunately, with an increasing population putting greater demands on resources, serious pollution incidents do happen periodically on our waterways. During the summer of 2013 on the River Thame below Aylesbury most of the fish were killed, and all of the dragonflies disappeared and didn’t return, following a major sewage release.


Because of this, and our wish to secure long-term improvements to the Thame, one of the major initiatives initiated by the Trust is 6-monthly liaison meetings with Thames Water at the Aylesbury Sewage Treatment Works to keep in closer touch with the company about the status of water and sewage management and to help them to spread information about how to manage domestic waste and water.

What is the problem with poor water quality?


A pipe discharging water in to the river, where could this be coming from?

Major pollution incidents usually result in rapid and dramatic changes to biodiversity in our river. They are usually noticed quickly and can make local or even national news, especially when large numbers of fish are killed. General pollution from road and agricultural run-off is different as it is gradual, and its origins can be very difficult to trace. Changes in such pollution usually go unnoticed until it is too late, and damage has been done.

Nitrates (mostly from agricultural run-off) and phosphates (often an indicator of sewage leaks) are two of the biggest pollutants in our rivers. They occur naturally in very small concentrations, but in the Thame and its tributaries they can be at very high levels, which affect both plant and animal life directly and indirectly.

Many species in our rivers depend on good water quality for their very existence, and even small changes in the concentrations of pollutants can wipe out an organism from an area, which then affects all the organisms that depend upon it. As the pollution increases, the number of species present tends to decrease until only the most pollution-tolerant organisms remain, such as red worms and bacteria.

Uncontaminated surface water tends to be very pure, which restricts plant growth, which in turn helps the flow of the stream, and the lack of bacteria and decomposition enables a high level of dissolved oxygen in the water. This is a very healthy state for fish and other aquatic animals.

Where the concentration of pollutants is high, plant growth is enhanced, which tends to slow down the flow, covers the surface in duckweed and algae, and also encourages the growth of bacteria that use up the dissolved oxygen. This is called eutrophication, which causes fish to move to where there is more oxygen, and kills the naturally occurring invertebrates who can’t migrate. The resulting loss of their food sources will cause other species, such as wetland birds and mammals, to move away or die.

The tiny protozoans, diatoms and crustaceans which are at the base of the food web are very sensitive to changes in water quality. Fish, frog and dragonfly larvae rely upon them completely, so their loss has a critical impact on biodiversity as a whole. You can learn more about how we use invertebrates to monitor our water quality by getting involved as a volunteer.


In-channel plants don’t always mean a bad thing, these submerged reeds are really important habitat and actually oxygenate the water!

How can we make a change?

There are a number of projects along the Thame that are endeavouring to improve water quality and biodiversity locally, but any serious pollution incident undermines this work. The Trust is working to secure long term improvements in the water quality and biodiversity of the River Thame which requires a political will in local and national government; however, we can make progress if we have the wholehearted involvement of the local community.   If you would like to help secure your river’s future, you can get involved by signing up as a volunteer.