There are currently no known warnings in place in Canterbury. Routine cyanobacteria monitoring in rivers has finished for the 2013-14 season and will resume in November 2014.
Potentially toxic, naturally-occurring cyanobacteria (blue-green algae) such as Phormidium, Oscillatoria, Lyngbya and Planktothrix are found in rivers throughout the country, but only form problematic thick blooms at some sites under the right flow conditions. In thick blooms, the dark mats can peel off the substrate and show a lighter-coloured underside. Although district or city councils may place signs warning of potentially toxin algae, these may not be seen at the numerous river access points, hence the need for people to treat every low-flowing river cautiously.
Blue-green algae form dense dark brown/black mats on river stones. When the mats break away, particularly after a downpour, they may accumulate at the river edge. Contact by skin or swallowing can cause rashes, skin and eye irritation, allergic reactions, gastrointestinal upset, and other effects in humans.
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