It's an ill wind that does not blow some good, especially if it is an invasive shellfish which has now spread from the Shannon to Lough Corrib.
The zebra mussel, which has been confirmed in the great western lake this week, consumes cryptosporidium - the parasite which prompted a serious five-month health alert when it infiltrated Galway's public water system earlier this year.
The Western Regional Fisheries Board (WRFB) says that the long-feared infestation of Corrib will have a significant impact on all aspects of the lake, from water supplies to ecology and fisheries. It says that the infestation appears to be "fairly widespread". The parent population and original infestation site has not been traced.
The zebra mussel is native to the Caspian Sea region of Asia, with a distinctive strip on its small shell. Cryptosporidium and other parasites causing illnesses such as giardia are on their menu list. Dr Dan Minchin, specialist in aquatic invasive species, says that cryptosporidium spores have been found in their shells. However, before local authority engineers believe this may solve all Galway's water contamination problems, Dr Minchin cautions that the impact of the zebra mussel is such that it could cause serious ecological difficulties.