Safe to swim?

Horizons Regional Council monitors the water quality at two spots at Waikawa Beach: in the river near the footbridge and on the sea shore. Check the results on their Safe Swim Spots map. Our readings are the first and first of the last in the table.

Example water quality readings.
Example water quality readings.

Measurements are for for E. Coli, Cyanobacteria and Enterococci.

Land, Air, Water Aotearoa (LAWA) – Beach and freshwater recreation monitoring says:

When contaminated by human or animal faeces water can contain disease-causing bacteria, viruses and protozoa (such as salmonella, campylobacter or giardia). These organisms can pose a health risk in water that is used for recreational activities such as swimming. The most common illness is gastroenteritis but respiratory illness and ear and skin infections may also occur. …

The quality of water for swimming is determined by measuring ‘faecal indicator bacteria’ (enterococci in coastal waters and E. coli in rivers and lakes) which indicate the levels of disease causing organisms in the water.

Land, Air, Water Aotearoa (LAWA) – Faecal Indicators says:

E. coli (Escherichia coli ) is a type of bacteria commonly found in the guts of warm-blooded mammals (including people) and birds. High E. coli concentrations in freshwater can be harmful to humans.

Common sources of E. coli bacteria are untreated human wastewater discharges, stormwater run-off and animal waste. Faecal concentrations are typically higher in pastoral streams but even near-pristine streams are not totally free from E. coli because of faecal deposition by birds and wild animals.

Enterococci are bacteria that naturally occur in the gut of humans and animals as well as birds, fish and reptiles. They are the preferred biological indicator for faecal contamination of coastal swimming sites. Enterococci are the bacterial indicator for Marine water.

Land, Air, Water Aotearoa (LAWA) – Cyanobacteria (blue-green algae) says:

Cyanobacteria (commonly known as blue-green algae) are microscopic organisms that play a very important role in many land and aquatic ecosystems. In aquatic environments cyanobacterial cells can multiply and form blooms in the river (planktonic) or dense mats on the river bed (benthic).

… an increasing number of cyanobacterial species are known to produce  poison or toxins. These natural toxins, known as cyanotoxins, can be a threat to humans and animals if consumed in drinking water or by contact during recreational activities. The effect of cyanotoxins varies from rapid onset of nausea and diarrhoea, to, in extreme cases, more serious effects such as liver damage.

Dog deaths associated with benthic cyanobacteria have become increasingly common around New Zealand. … Phormidium is an example of a cyanobacteria species that can produce cyanotoxins and has been responsible for over 70 dog deaths in New Zealand in the last decade.

See also: The river runs red.