SWIMMING in rivers could be off the fun list this summer, with many of Southland’s swimming spots failing government standards for bacterial (E. coli) counts, University of Canterbury and Lincoln University hydrogeologist and aqueous geochemist Dr Clint Rissmann says.
Environment Southland (ES) staff also found toxic algae in the Aparima River at Thornbury last week, and in the mid-Mataura River last month.
ES freshwater and marine science leader Nick Ward said the long-term forecast was for a long, hot summer, which meant a high likelihood of more occurrences of toxic algae blooms in Southland waters.
ES director of science and information Graham Sevicke-Jones said for E. coli bacteria testing, two standards were used to measure recreational water quality: “secondary contact”, where full immersion was unlikely, for example fishing or boating, and “primary contact”, where it was likely a person’s face would be in the water.
“Samples from sites are reported in bands – A band being very good, through to D band, which is poor.”
In Southland, for secondary contact, 25 sites were in A band, 20 in B band, four in C band and six in D band, he said.
However, Dr Rissmann said the banding method was only for secondary contact and was not up to date with current government requirements for assessing a river’s suitability for swimming during the summer months.
For swimability, the Government advised a specific testing method which used multiple repeat measurements during the summer months to classify a site.
“If this more robust method is used, all of Southland’s lowland sites fail the primary and secondary contact guidelines,” Dr Rissmann said.
E. coli was only an indicator of a much wider range of microbes such as viruses, which were not measured.
Water temperature rises and lots of sunlight could trigger a more rapid growth of algal species, he said.
Mr Sevicke-Jones said the safety of activities such as boating and canoeing depended on the amount of direct contact people had with the water.
“If you swallow the water or your skin is in contact with the water, you are at risk of a reaction to any toxic algae which may be present.”
Boats, canoes and life jackets should be washed down with clean water after use, he said.