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River water quality

Water Pollution Act 1993

In order for the river quality to be maintained and possibly improved in the face of increased developmental pressures, it is necessary to exercise controls over the discharges to our rivers.

This requirement has been recognised for some time and, as a result, the Water Pollution Act (1993) was enacted under section 5 during early 2005 to enable the issuing of licences for discharges of trade and sewage effluent, the taking of legal proceedings for discharging effluent without or in breach of the conditions of a licence, and the provision for setting regulations for preventing pollution.

River quality

River quality monitoring is undertaken during spring, summer and autumn every year at 87 monitoring sites. Various parameters are assessed including biological, chemical and heavy metals.

Biological monitoring (invertebrate sample) is undertaken using the kick sampling method. This sampling method is undertaken three times per year to provide long term data on the water quality. The presence or absence of particular invertebrate species is influenced by the water quality over a period of time and is representative of overall site health.

A chemical water sample is a sample collected from a monitoring site and provides data on the water quality at that specific time. Results will vary depending on the flow conditions and might miss individual pollution events. The water samples will be analysed by the Government laboratory for the following parameters; biochemical oxygen demand, alkalinity, ammonia, nitrate and phosphate.

Due to the natural geology and mining history on the Isle of Man it has been suggested to introduce heavy metal environmental quality standards which will be monitored at specific sites.

SeasonNumber of Sites
Biological MonitoringChemical MonitoringHeavy Metal Monitoring
Spring (Mar – May) 31 31 13
Summer (Jun- Aug) 31 87 13
Autumn (Sep – Nov) 31 31 13
Winter (Dec – Feb) 0 87 13
Total Samples 93 235 52

In the latest summary monitoring report for data from 2015-2019; 95% of sites achieved ‘Very Good’ classification for chemical water quality. Phosphate concentrations across the Isle of Man are generally ‘Very Low’. However nitrate concentrations across the island are elevated due to nutrient run off from land. Further investigations will be carried out into the source of the nitrate and where necessary the Department will work with stakeholders to reduce the impact of nitrate on watercourses. For a more detailed summary of water quality please see the most recent report.

For further information, please contact +44 1624 685885 or email

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