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Government of

Information and public services for the Island of Jersey

L'înformâtion et les sèrvices publyis pouor I'Île dé Jèrri

Freshwater species monitoring

The freshwater monitoring scheme evaluates the water quality of Jersey's streams. The scheme bases its study on communities of macroinvertebrates in the streams.

Macroinvertebrates are small animals living in water that have no backbone and are visible with the naked eye ie no magnification necessary.Common examples of macroinvertebrates are freshwater shrimps and snails. As well as larval stages of land-based flying insects such as:

  • caddis flies
  • dragonflies
  • mayflies
  • damselflies

The presence of macroinvertebrates

It may be difficult to identify stream pollution with water analysis, which can only provide information for the time of sampling. Even the presence of fish may not provide information about a pollution problem because fish can move away to avoid polluted water and then return when conditions improve. However, most stream-bottom macroinvertebrates cannot move to avoid pollution. A macroinvertebrate sample may therefore provide information about pollution that is not present at the time of sample collection. Many types of pollutants can affect macroinvertebrates eg the bacteria that break down sewage can use up oxygen from the water that macroinvertebrates need in order to survive.

Monitoring process

  • the monitoring is conducted during specific times of the year to reflect the life cycles of different families of macroinvertebrates
  • each monitoring site consists of a 20m stretch of stream which is carefully recorded so that the exact same 20m stretch is used each time
  • information is collected about the width of the stream, the depth of water and its rate of flow, the type of material on the bottom of the stream and the vegetation growing along the banks
  • field analysis is also carried out to determine the pH of the water, its temperature and how much oxygen present
  • finally, a sample of the stream life is collected using a standard 3 minute kick sample method, in which material from the stream is kicked into a specially designed handnet. This is then taken to a laboratory where the families of macroinvertebrates are identified and recorded


To find out results and learn more about the monitoring scheme see the links below:
Quinquennial review of Jersey flowing waters  

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