Health Warning – Algal Bloom in Kaiapoi Lakes, Ashley/Rakahuri River and Lake Pegasus

Updated 18 February 2020: Following formal health warnings for the Ashley/Rakahuri River at SH1 and Pegasus Lake, algal blooms have also been found in the eastern lake of the Kaiapoi Lakes, and from 18 February toxic algae is also present in the length of Ashley/Rakahuri River from Okuku River confluence to Ashley SH1.

18 February Update 5.15pm: Canterbury District Health Board have issued a health warning for the length of Ashley/Rakahuri RIver from the Okuku River confluence to Ashley SH1. Follow this link to find out more https://tinyurl.com/ul5nrr9

18 February update: While the Canterbury District Health Board's Community and Public Health unit lifted the algal bloom health warning at the Ashley/Rakahuri River at the Rangiora-Loburn Bridge on 10 February, ongoing warm and dry conditions as well as low flows could change the situation at short notice. Therefore as an extra precaution the warning signs at the Ashley/Rakahuri River at Cones Road will be in place until further notice.

ECan's Water Science Team have discovered cyanobacteria at another location in the Ashley/Rakahuri River, just south of the Okuku River confluence (off Mt Thomas Road). Signage is in place to warn river users of its presence.

10 February update: Canterbury District Health Board’s Community and Public Health unit has lifted its algal bloom health warning issued for the Ashley/Rakahuri River at the Rangiora-Loburn Bridge (also called the Cones Road Bridge). This was issued on 6 January 2020.

Canterbury Medical Officer of Health Dr Alistair Humphrey says Environment Canterbury’s sampling of the Ashley/Rakahuri River at the Rangiora-Loburn Bridge will continue to the end of March and then will resume at the beginning of next summer when there is increased likelihood of cyanobacteria growth.

A health warning for the Ashely/Rakahuri River at SH1 remains in place.

3 February update: Water testing by ECAN has confirmed the presence of potentially toxic algae (benthic cyanobacteria) in the eastern lake of the Kaiapoi Lakes. Although this testing has confirmed the presence of the potentially toxic algae in only the eastern lake, recreational users are advised to treat the whole of the Kaiapoi Lakes area with caution.

This follows formal health warnings for the Ashley/Rakahuri River at SH1, the Ashley/Rakahuri River at the Rangiora-Loburn Bridge (Cones Road Bridge) and Lake Pegasus, all of which are still in place as at 3 February.

People should avoid these areas and keep their animals, especially dogs, away from the water until the quality has improved and warnings are lifted.

27 January update: Canterbury District Health Board’s Community and Public Health unit has issued a health warning for the Ashley/Rakahuri River at SH1.

The warning follows testing that showed high levels of potentially toxic algae (benthic cyanobacteria) upstream of the SH1 Bridge in the Ashley/Rakahuri River.

This follows earlier warnings for the Ashley/Rakahuri River at the Rangiora-Loburn Bridge (Cones Road Bridge), as well as Lake Pegasus, where is was discovered in early January to have potentially toxic algae (planktonic cyanobacteria) in the water.

People should avoid the area's above and animals, particularly dogs, should not be allowed near the water until the health warnings have been lifted.

There are also other access points along the Ashley/Rakahuri River that may have benthic cyanobacteria present. People are advised to treat every low-flowing river cautiously, check for the presence of benthic cyanobacteria and avoid contact (the You Tube video below tells you what to look out for).

Canterbury Medical Officer of Health, Dr Ramon Pink says the algae look like dark brown to black mats and can produce toxins harmful to people and animals.

“Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips.

“If you experience any of these symptoms, visit your doctor immediately, also let your doctor know if you’ve had contact with dark brown/black algal mats or water in this area,” Dr Pink says.

Reticulated town water supplies are currently safe but no one should drink water from the river at any time. Boiling the water does not make the water safe.

Pets that show signs of illness after coming into contact with algal mats should be taken to a vet immediately.

Environment Canterbury is monitoring the sites and the public will be advised of any changes in water quality.

Facts about cyanobacteria:

  • Appears as dark brown/black mats attached to rocks along the riverbed.
  • A low cover of the algae can occur naturally but can increase rapidly during warmer months. Algal blooms are influenced by a combination of available nutrients in the water and sediments (such as nitrogen and phosphorus), a sustained period of low and stable flows, and favourable weather conditions (e.g. increased temperature, calm days).
  • It often has a strong musty smell and algal toxin concentrations can vary over short periods.
  • Although high river levels will remove the algal bloom, detached mats can accumulate along the shore and increase the risk of exposure to toxins.
  • If a health warning is in place avoid contact with the water.
  • Although district or city councils may place warning signs, these may not be seen at the numerous river access points, hence the need for people/ dog-walkers to treat every low-flowing river cautiously.

For further information visit

https://www.lawa.org.nz/explore-data/canterbury-region/

Or contact Community and Public Health on (03) 364 1777:

https://www.cph.co.nz/your-health/recreational-water/

For more information about Mahinga Kai:

https://www.cph.co.nz/wp-content/uploads/saf0112.pdf

Learn more:

Toxic Algae Information Brochure