THE quality of island streams has improved in the past five years, according to Guernsey Water.

The number and variety of invertebrates in 19 streams is recorded and water quality technician Sarah Brown said this benthic survey had shown year-on-year improvement.

Miss Brown collects and studies the invertebrates in the water, including freshwater shrimps, leeches, snails and larvae.

These creatures are an indication of any pollution because they cannot move from the source.

‘Generally, pollution is caused by run-off from farming, overflowing cesspits or oil spillage,’ said Miss Brown (pictured). ‘The number of types of creatures in the water is a good indication of whether there are any of these problems.’

The quality of stream water often depends on its location. The cleanest runs down to Fermain and is isolated from human activity. It can support mayfly larvae, which are very sensitive to pollution.

The dirtiest of the 19 is a stream near La Vrangue. It is close to houses, which increases the likelihood of contamination.

The surveys are carried out in spring and autumn every year and Miss Brown hoped the results would continue to improve.

‘We are making a concerted effort to make people aware of their pollution and that these streams are our potential drinking water.’