The regular summer weekly monitoring programme for potentially toxic benthic cyanobacteria such as Phormidium ceased on March 1st 2012. However, recreational river sites with existing warnings will continue to be surveyed until the warning status has been downgraded.
Warnings in place – 2nd April 2012
The latest surveys indicate that potentially toxic cyanobacteria growths are either increasing or that mats are detaching and accumulating on shore, at the following sites:
Hurunui District
Waiau River Bridge at Waiau Township - A recent survey (week commencing March 19th 2012) indicated high levels of potentially toxic cyanobacteria. River users should avoid swimming or walking their dogs in areas where mats are detaching and/or accumulating at the river edge.
In general
When conditions are warm and flow is low and stable, there is an increasing risk of benthic cyanobacterial mat growths at some of our surveyed sites. However, after sufficient fresh flows, scouring may wash off mat growths.
This web page will be updated if the status changes, or you can check our Facebook page.
About Phormidium (algae)
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.
Amongst green algae
Within riffles
At the river edge
Attached to rocks
Dried
Phormidium
In shallow water
Toxic algae on rock
