River Tees

The River Tees rises on the eastern slope of Cross Fell in the upper Teesdale region of the North Pennine Area of Outstanding Natural Beauty (AONB). It is 85 miles in length, has a catchment area of 1834km2 and flows generally eastwards to meet the North Sea between Hartlepool and Redcar.

Numerous hills surround the river’s source, some exceeding 2500ft, and the landscape is bleak with large expanses of blanket bog and heather moorland. The head of the Tees is dammed to form Cow Green Reservoir, our highest reservoir at an altitude of 480m. The reservoir is used to make regulatory releases into the River Tees to allow abstraction to take place downstream, where the landscape becomes more hospitable opening out into green dales. Here agriculture dominates; predominantly pasture for beef and sheep rearing with arable in the more fertile lowlands. The Tees flows through a number of towns and villages before it reaches our abstraction point at Broken Scar Water Treatment Works on the western edge of Darlington. The Tees has a number of major tributaries including the Rivers Lune and Balder, both of which have been dammed to create a series of reservoirs which supply our Lartington Water Treatment Works.

Image courtesy of North Pennines AONB Partnership.

River water quality

A vast area of the upper Tees catchment is blanket bog. Like many peatlands, drainage channels known as ‘grips’ were historically dug to improve drainage and make the land more suitable for sheep grazing. However, this has resulted in the water draining from the uplands being a tea-like colour, caused by dissolved organic carbon (DOC), which leaches from the peat. Furthermore, the increased drainage has lead to the peat drying out and being eroded by the weather, resulting in even more DOC being carried off the land and into the river. The DOC must be removed by the water treatment process, which is costly and produces a large amount of sludge that must itself be treated and disposed of.

The Tees Water Colour Project

The Tees Water Colour Project was set up in 2005 and aimed to reduce water colour in the River Tees by focusing on management of the upstream catchment, none of which Northumbrian Water owns. Blocking the grips was seen to be the solution to reducing the leaching of colour from the bogs. In order to block the grips, we needed to work with all stakeholders including landowners and managers, the Environment Agency, Natural England, Defra, RSPB and the North Pennines AONB Partnership. The first grip was blocked in 2008, with 68km of moorland grips being instated in total.

Monitoring has been carried out by Durham University and a decrease in the amount of DOC leaching from the blocked grips compared to the remaining unblocked grips has been shown. The grip blocking had the additional benefit of restoring 196ha of SSSI blanket bog, which is particularly important as a habitat for wildlife and may play a role in flood control and as a carbon store, which if lost would contribute to climate change severity.

Monitoring continues and it may be several years before the true success of the project can be quantified.


We work with the relevant stakeholders in the catchment, including the Tees Rivers Trust, Natural England, the Environment Agency, local farmers and landowners. We have maintained an ongoing partnership with the North Pennines AONB Partnership, supporting their work to restore the eroded areas blanket bog in the Tees catchment.

Your catchment advisor

Rob Cooper is Northumbrian Water’s Catchment Adviser for the River Tees. Rob has a First Class Honours degree in Countryside Management from Aberystwyth University. He has worked on a number of farms whilst at university; and upon graduation worked as a research assistant for the university on a number of Defra research projects, looking at biodiversity and ecosystem services. Following this, Rob worked in a number of roles for the Farming and Wildlife Advisory Group (FWAG) in the East of England, including as Norfolk and Suffolk coordinator for the Campaign for the Farmed Environment (CFE).

Catchment management


Northumbrian Water′s catchment management work aims to prevent deterioration and then improve the quality of water in the rivers and lakes that we abstract from the drinking water supply. Find out more

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