As summer continues, dog owners, parents and people who are immune-compromised are being reminded about the risks of toxic algae in rivers.
Tasman District Council communications officer Tim O’Connell says recent rain may have dislodged algae matting and washed it downstream. As the river levels drop, these mats can gather near pools, banks and low-flow areas where they pose a higher risk.
The alga is natural and occurs during extended periods of low river flow, forming gelatinous mats on the riverbed. It can have a distinctive musty smell that is attractive to dogs.
Council monitors its presence at least weekly during the summer toxic algae season on the Wai-iti, Lee, Roding and Tākaka Rivers, with other rivers monitored monthly. Tim says the Wai-iti River is considered a ‘sentinel site’, as it tends to provide the earliest warning that levels of toxic algae are increasing. The latest water quality and toxic algae results are reported on the Tasman District Council website here.
When toxic algae levels at the Wai-iti site reach 20 per cent, the council samples additional sites. Since November, testing at the Wai-iti site has remained in single figure percentages, apart from a 10 per cent sample on 5 January which was subsequently followed by a four percent sample a couple of days later.
The latest recording on 12 January was 3.75 per cent, which is well below threshold levels. If dog owners see toxic algae present, he says it would be wise to put dogs on a lead and prevent them from scavenging or playing in or near the water.
Historically, the Roding and Lee rivers have consistently very low coverage of toxic algae and he says they are indicative of most Tasman rivers. When toxic algae levels are high, warning signs are posted at popular access routes to rivers, based on results of the monitoring.
