River Thame Catchment Water Quality Analysis 2017

Last week we were invited to share an evening event with Freshwater Habitats Trust in Aylesbury, where they celebrated their fantastic achievements throughout their Clean Water for Wildlife Project – a three-year national project using Citizen Science to monitor water quality.

We presented what we have learnt so far through Citizen Science about the water quality of the River Thame Catchment. For those that couldn’t make it, here is a snapshot of the results collected by our team of dedicated volunteers since we started monitoring in 2014.

Collating all data collected by RTCT volunteers, RTCT staff and Freshwater Habitats Trusts Clean Water for Wildlife Project, we have 1887 records  throughout the Thame catchment. They are gathered over 290 sites (many are multiples on same sites over time).

These results have been analysed by the River Thame Catchment Partnership.


The black dots on this map represent all sample points so far. You’ll see we have made a good start on covering a large number of tributaries of the Thame and the main river but we can see some gaps on the waterways; particularly in the north of the catchment.
The purple dots show the locations of ponds throughout the catchment; we can see we have masses! But these have been generally under surveyed so far.

The pie chart below shows the proportion of water bodies that have been monitored or surveyed since 2014. It’s clear there has been a focus on the main river and streams.

What is the picture so far?

The map below shows the sites that have been tested so far that are clean, have some pollution and those that are highly polluted. 





74% of the sites that have been surveyed so far have been highly polluted with nitrate, with only 15% being free from nitrate pollution. Nitrate pollution generally comes from runoff of fertilisers from agricultural land. This result isn’t surprising as it is well known that underground aquifers in the catchment are highly polluted with nitrate from centuries of fertiliser use.
Phosphate is a more positive picture with 41% of sites being clean and 44% of sites being highly polluted. Phosphate can be found in huge quantities in our running water due to discharges from sewage treatment works. Phosphate also attaches itself to soil particles meaning any sediment loss from agricultural land can also have detrimental effects on the phosphate concentrations in our water courses.

Combining both nitrate and phosphate data together means that a staggering 83% of the sites sampled are highly polluted, with only 8% being free of any pollution.

Although this is a sad picture for the main river and many of it’s main tributaries let’s think about some of the positives of these results!

  • It’s just as important knowing where the highly polluted sites are as knowing where the clean sites are. All the data collected will help us to inform our work and where to focus efforts.
  • There are quite a lot of gaps in the catchment, particularly in the head waters and small streams where it’s likely the clean water will be found.
  • The results of Freshwater Habitats Trusts, Clean Water for Wildlife project showed that much of the clean water is found in ponds, we haven’t even touched the surface with surveying these yet!

Our results are similar to most lowland catchments in England. Nitrate pollution is often common in agricultural catchments such as ours, so we are not alone in our fight against nutrients!







Why is long term monitoring important?

Long term monitoring can show variations in pollution over time. Seasonal changes, rainfall levels, change in land practice all have an impact on pollution levels so sampling just once doesn’t give a true picture. Long term monitoring will also show whether the work we are doing is having a positive impact on water quality.

For example, the Cuttlebrook which is a tributary of the Thame and runs through Cuttlebrook Nature Reserve in Thame. 10 sites on the brook have been monitored regularly since October 2014 by the Cuttlebrook volunteers. Our analysis shows (see graph below) that 6 out of the 10 sites have been clean at least once, but all have been polluted at some point in that time frame. We will be looking into other sites that have been monitored for long periods of time to find out what could have caused these huge differences in the water quality at these sites.


What now?

We have decided the best way to get more coverage of the catchment is to carry out a Water Blitz in spring 2018 (dates to be arranged) within a 6 week period. A water blitz is when you try and get as much data of all water body types throughout the catchment as possible over a short period (to avoid seasonal changes). This includes; springs, ditches, ponds, headwater streams and of course the main river.

All of your data from your regular testing sites will be included in the Blitz but if you would like to sign up for one-off additional sites please email Enquiries@RiverThame.org to register your interest. We’ll need all hands on deck!

Final word

From us all at the Trust we would like to thank the volunteers who have put a lot of time and effort into collecting this massively important data for us. Please do keep up your hard work, it is very much appreciated. As cheesy as it is, we really could not do it without you!

Lets go find some more clean water!