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Our Results

See the results of our testing in our monthly report:

OART test the water quality at 8 locations in the Sussex River Ouse catchment on a monthly basis.

Where we Test

For maps showing where the sample sites are, please use the links below:

Longford Stream

A - South Rd
B - Beresfield Lane
C - A275, Chailey
E - Cockfield Bridge
G - Longford Bridge


Water Quality Monitoring
Waste Water Treatment Works

One of the many Waste Water Treatment Works in the catchment

Why Is It Important To Monitor Water Quality?

  • 38 major sewage treatment works are located on the Sussex Ouse and its tributaries.
  • Risk of pollution not from harmful bacteria or solid waste but dissolved nitrates, phosphates and other harmful chemicals.
  • High levels of these chemicals can lead to the destruction of the rivers rich variety of wildlife.
  • Increasing population in the South East increases the demand to put more treated or partially treated waste into the rivers.
  • Effects exacerbated in summer when there is less water to dilute the waste
  • In times of heavy rain sewage treatment works can’t always cope and raw sewage flows into the rivers.
  • Some farmland along the rivers is ploughed to the banks, allowing fertilisers to easily ‘run-off’ into the water, making the situation worse.

The Story So Far:

OART (formally SOCS) have been taking water samples regularly from the Bevern, Plumpton Mill & Northend Streams since May 2001. Some of the original sites showed no significant failure of water quality and have been substituted for other sites, although the original data has been retained. More recently, further sites on the rivers Ouse & Uck along with many of their tributaries have been included. All these new sites are on the section of the river Ouse which has been designated as a salmonid water under the EU Freshwater Fisheries Directive.

The purpose of this sampling is to:

  • Monitor the chemical content of the water within our rivers
  • Where and when necessary provide evidence of quality falling short of standards laid down by the EC Freshwater Fish Directive, for both salmonid and cyprinid (coarse) fish.
  • Help to identify isolated pollution incidents and all our information is passed to the Environment Agency for investigation.

What We Do:

A minimum of 12 (monthly) water samples are collected in clean glass bottles (to avoid cross contamination) from each site and taken back to our ‘in house’ (literally) laboratory! At least 12 samples are collected in order that a true picture of the quality can be ascertained with information from each site calculated as an average. Where untoward results are obtained, the period of testing is extended to provide further evidence of a problem.

Tests are carried out using standard scientific test equipment (ion specific meters) designed to measure concentrations of ammonia (usually from sewage effluents), phosphate (from sewage and, to a lesser extent, agricultural fertilisers) and dissolved oxygen. Since 2007 we have also measured the amount of nitrogen derived from the nitrates in our samples. These are also present in sewage effluents & agricultural fertiliser and their presence, in significant amounts, causes eutrophication along with potential health risks from their presence in drinking water. Although the EU Freshwater Fisheries Directive does not set parameters for nitrates but for nitrites (NO2) it gives guide values as shown in the table below. Recently we have added measurements of conductivity and pH to our testing regime. Conductivity measures the total ionic concentration in the sample, so includes salts such as sulphates, chlorides etc. and pH is a measurement of acidity or alkalinity of the water.

The results from the water quality testing are published in our monthly Water Quality Report as they become available; the latest results are available by clicking here or from the side menu.

Collecting a water sample

Collecting a water sample to be tested

Analysis of water samples at our in house laboratory

Analysis of water samples at our in house laboratory

It is now our aim to extend this monitoring to the river Adur. In order to do so we need your help, if you live in the Adur catchment and would like to take part in collecting samples on a monthly basis then please let us know at

Ammonia < 0.4 mg/l N
Phosphate < 4 mg/l PO4
Nitrate < 5mg/l NO3
Dissolved Oxygen > 4 mg/l O2

OART designated acceptable limit values

OART has designated acceptable limits for the chemical composition of the water within the Ouse and its tributaries. These values have been chosen to reflect what can be reasonably expected within the catchment. These values are a variation of those set out by the EU Freshwater Fisheries Directive which are set out below.

EU Freshwater Fisheries Directive Guide values

  Salmonid Cyprinid
Ammonia (as N) < 0.03 mg/l < 0.16mg/l
Phosphate < 0.2 mg/l < 0.4mg/l
Nitrate < 0.01 mg/l < 0.03 mg/l
Dissolved Oxygen 50% saturation > 9mg/l
100% saturation > 7mg/l
50% saturation > 8mg/l
100% saturation > 7 mg/l

The dissolved oxygen in pure chalk spring water can vary from 12 mg/litre at 5 degrees centigrade to 8 mg/litre at 25 degrees. The amount of dissolved oxygen present depends upon the temperature. Organic matter (pollution) can consume some oxygen and the water is then partially saturated. The minimum acceptable concentration is 4 mg/litre. Water with 4 mg/litre at 25 degrees would be 50 %saturated (4/8 x100). The percentage saturation is therefore a measure of pollution. Most samples we test are between 50 to 70 % saturated.


  Salmonid Cyprinid
Ammonia (as N) < 0.78 mg/l < 0.78mg/l
Dissolved Oxygen 50% saturation > 9mg/l
100% saturation > 6mg/l
50% saturation > 7mg/l
100% saturation > 4mg/l
Phosphate No mandatory limit No mandatory limit

EU Freshwater Fisheries Directive Mandatory values

The Freshwater Fisheries Directive also lays down mandatory parameters for dissolved oxygen and ammonia. These are shown in the table on the right. Note: There is no mandatory limit laid down for the phosphate or Nitrate levels in lotic waters.