Cyanobacteria can be harmful to people and dogs. Cyanobacteria can be found in rivers and lakes and is likely to present as algal mats ( Benthic Cyanobacteria) or free floating in lakes and ponds (Planktonic Cyanobacteria) .

Benthic CyanobacteriaPlanktonic Cyanobacteia
Benthic CyanobacteriaPlanktonic Cyanobacteria

Blooms form when cyanobacteria start to multiply very quickly, usually due to changes in environmental conditions such as warm temperatures, sunlight, low or stable river flows, and high levels of nutrients.

For cyanobacteria, avoid water that is cloudy, discoloured, musty smelling, or has small globules, coloured scrum or thick dark brown/black mats on the bed of the river, with a slimy velvety texture.

For up to date information on the Selwyn rivers and the status of the rivers in regard to if the water is swimmable, visit the LAWA website. This website also gives the current updates in regards to E.coli or faecal contamination at each site, this can also make the water unsuitable for swimming.