River water quality

• Biological river water quality has been consistently good in the South West, in 2008 88% of the biology network was classified in the top two quality bands.
• Chemical river water quality has also been high since 1990 with the percentage of river stretches classed as very good or good reaching a peak of 91% in 2000.  In 2008 this now stands at 89%.
• Nutrient levels are falling.  Stretches of rivers in the South West recording high phosphate concentrations have reduced from 54% in 1990 to 41% in 2008.  Stretches with high nitrate concentrations have remained around 26% for the last few years, however in 2008 this fell to 24%, only 2 percentage points away from the 22% recorded in 1990.  

Data available on this page is to South West Government Office Boundary and so figures may vary from figures produced for the Environment Agency South West Region.

The quality of water in our rivers is monitored by the Environment Agency in order to assess the overall health of the inland water ecosystem. It is one of the 68 indicators of the Government’s Sustainable Development Strategy.

River water quality can be influenced by a wide range of factors:

• Variations in rainfall and river flow can have a significant effect - lower than average rainfall and low river flows can result in poorer water quality as there is reduced dilution of pollutants
• Low river flows and warm temperatures can result in the growth of algae, which affects dissolved oxygen demand in rivers
• High rainfall can also adversely affect river quality by causing increased leaching of pollutants in the soil. Overflows from the sewerage system can also occur during periods of particularly intense rainfall
• Increased river flows can also improve river water quality however, by increasing the dilution of pollutants

The way the Environment Agency measure water quality is changing. For twenty years, a general quality assessment (GQA) scheme has been used to assess river water quality in terms of chemistry, biology and nutrients. GQA has helped drive environmental improvements by dealing with many of the major point sources of pollutants, such as discharges from sewage treatment works or other industry. We now need a more sophisticated way of assessing the whole water environment that will help us direct action to where it is most needed.

The European Water Framework Directive (WFD) will give us the means to do this by looking at over 30 measures, grouped into ecological status (this includes biology as well as ‘elements’ like phosphorus and pH) and chemical status (‘priority substances’). The WFD covers estuaries, coastal waters, groundwater and lakes as well as rivers.  More information about the Water Framework Directive is available on the Environment Agency website.

Biological river water quality

National biological quality

The Environment Agency want to see as many rivers as possible in the top two quality bands of excellent or good. In 2008, 72% of English rivers were at this level – , compared with 55% in 1990. 88% of Welsh rivers were of good or excellent quality, compared with 79% in 1990. The Environment Agency website has further information.

South West biological quality

The water quality in the South West has been consistently good, with around 88-90% of the biology network classified as very good and good since 1995.

The map shows that biology water quality is good across the region In 2008 88% of the stretches were graded very good or good. The majority of the stretches graded fair to bad are located in the North of the region

Chemical river water quality

National chemical quality

The Environment Agency want to see as many rivers as possible of excellent or good quality. In 2008 79% of English rivers were at this level compared with 55% in 1990. 95% of Welsh rivers were of good or better quality – the best on record, compared with 86% in 1990. The Environment Agency website has further details.

South West chemical quality

The Chemistry quality has also been high since 1990 with the percentage of river stretches classed as very good or good reaching a peak of 91% in 2000 before reducing slightly to 87% in 2007.  Since then water quality has improved with figures now released for 2008 showing an improvement of 2 percentage points to 89%.  No rivers were graded bad.

The chemistry map shows that water quality is good across the region. No stretches were graded bad, however the Somerset Levels contain many of the stretches graded fair to poor in the region.

Phosphates

National phosphate status

The Environment Agency want to see as few rivers as possible with high concentrations of nutrients, that is greater than 0.1mg/l for phosphate.

In 2008, 52% of English rivers had high concentrations of phosphate compared with 69% in 1990 and 9% of Welsh rivers had high concentrations of phosphate, compared 26% in 1990.

South West phosphate status

Stretches of rivers in the South West recording high Phosphate concentrations have reduced from 54% in 1990 to 41% in 2008.

The Phosphate map shows that rivers in the east part of the region record the highest concentrations. 47% were graded with very low or low concentrations.

Nitrates

 National nitrate status

The Environment Agency want to see as few rivers as possible with high concentrations of nutrients, that is greater than 30mg/l for nitrate.

High concentrations of nitrate were found in 32% of English rivers compared with 36% in 1995. High concentrations of nitrate rarely occur in Welsh rivers. The Environment Agency website has further details.

South West nitrate status

Stretches recording high nitrate concentrations have increased from 22% in 1990 to 26% in 2007.  In 2008 this figure fell by 2 percentage points to 24%.

The nitrate map shows that generally  the rivers in the East of the region record higher concentrations. 46% are graded very low to moderately low with a further 30% having moderate concentrations.

• Environment Agency river water quality
• What's in your backyard - find out about water quality in rivers near you
• Water Framework Directive