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BMWP Scoring - Measuring Freshwater Quality

Freshwater macroinvertebrates require various given amounts of dissolved oxygen in stream water in order to live, and organic or chemical pollution will reduce the oxygen level of water.

We use this knowledge, together with something called the Biological Monitoring Working Party (BMWP) scoring system to evaluate a stream or river and assign a quality category to it.  

BMWP scores reflect the sensitivity of macroinvertebrates to oxygen depletion.  So the number and type of species in the stream is a good indication of whether it is impacted by organic or chemical pollution.

The quality category is based on the scale below:

BMWP score

Category

Interpretation

0-10

Very poor

Heavily polluted

11-40

Poor

Polluted or impacted

41-70

Moderate

Moderately impacted

71-100

Good

Clean but slightly impacted

>100

Very good

Unpolluted, unimpacted

 

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