Regular weekly monitoring for potentially toxic benthic cyanobacteria such as Phormidium began 14 November 2011. A number of recreational river sites are surveyed in the region, including sites where growths have been observed in previous years such as in the Ashley River/Rakahuri, Selwyn River/Waikirikiri and Opihi River.
Warnings in place – 10th February 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
Hurunui River at State Highway 1 Bridge - Based on a recent survey (February 7th 2012), high growth of potentially toxic cyanobacteria has been observed downstream of the bridge. Mat growths have become prominent on cobble stones at the edge of the river as flows have receded. River users should avoid swimming or walking their dogs in areas where mats are detaching and/or accumulating at the river edge.
Waipara River at Stringers Bridge – Based on recent surveys (week commencing February 7th 2012), low to moderate growth of potentially toxic cyanobacteria has been observed with some mats detaching. Mats growths are prominent as river flows remain low and stable. River users should avoid swimming or walking their dogs in areas where mats are detaching and/or accumulating at the river edge.
Waipara River at Teviotdale Bridge – Based on recent surveys (week commencing February 7th 2012), moderate growth of potentially toxic cyanobacteria has been observed with some mats detaching. Growth has remained at a relatively high level because of sustained high temperatures and low flows. River users should avoid swimming or walking their dogs in areas where mats are detaching and/or accumulating at the river edge.
Waimakariri District
Waimakariri River, Reids Reserve - a recent survey (week commencing February 7th 2012) showed moderate growth of potentially toxic cyanobacteria with mats becoming exposed, particularly in the vicinity of the middle shingle bank. River users should avoid swimming or dog walking in this area where mats are obvious.
Ashley River/Rakahuri at Rangiora-Loburn Bridge – Based on recent surveys (week commencing February 7th 2012), moderate growth of potentially toxic cyanobacteria has been observed with mats detaching and accumulating as a thick layer on the river's edge. Mats growths have also been observed upstream of the swimming hole. River users should avoid swimming or walking their dogs in areas where mats are detaching and/or accumulating at the river edge.
Ashley River/Rakahuri at State Highway 1 Bridge - Based on recent surveys (week commencing February 7th 2012), moderate growth of potentially toxic cyanobacteria has been observed with mats detaching and accumulating on the river's edge. River users should avoid swimming or walking their dogs in areas where mats are detaching and/or accumulating at the river edge.
Ashburton District
Ashburton River/Hakatere - State Highway 1 Bridge - Based on recent surveys (week commencing February 7th 2012), growth of potentially toxic cyanobacteria mats is high with observations of mats detaching. River users should avoid the area, particularly where mat growths are obvious. Dogs should also be restrained to prevent contact with mats.
Timaru / Waimate Districts
Pareora River at Huts – The latest survey (week commencing February 7th 2012) indicates moderate-high benthic cyanobacterial growth, with mats detaching and accumulating along the river’s edge. Growth has remained high because of low flows and elevated temperatures. River users should avoid swimming or walking their dogs in areas where growths are obvious or accumulating on the river’s edge.
Opihi River at State Highway 1 Bridge – The latest survey (week commencing February 7th 2012) indicates moderate benthic cyanobacterial growth, with mats detaching. Once again, flow recessions and increasing temperatures have likely contributed to mat growth. River users should avoid swimming or walking their dogs in areas where growths are obvious or accumulating on the river’s edge
Opihi River at Saleyards Bridge – The latest survey (week commencing February 7th 2012) indicates moderate benthic cyanobacterial growth, with mats detaching. River users should avoid swimming or walking their dogs in areas where growths are obvious or accumulating on the river’s 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
