With warmer weather arriving and more people heading to their favourite rivers, lakes and beaches, the Otago Regional Council is launching its annual summer water monitoring programme this month.
Each year, the council’s environmental monitoring team collects weekly samples from popular freshwater and coastal swim spots to check whether the water is safe for swimming and other recreation.
"This work is about ensuring people have the knowledge they need to make safe choices before heading out for a swim", council water quality scientist Helen Trotter said.
"Our team visits 36 sites every week over summer to test for bacteria and check for signs of toxic algae (cyanobacteria). It’s a big effort, but it’s essential for keeping communities safe."
Monitoring of the 36 sites will continue until March 31.
Results are updated on Lawa (Land, Air, Water Aotearoa), a national platform that brings together water-quality information from councils across New Zealand.
Ms Trotter said water quality could change quickly, especially after rain.
"Rain can wash contaminants into waterways and lead to a temporary increase in bacteria levels. Avoiding swimming for 48 hours after rain allows time for bacteria and other harmful bugs to dilute and settle out, while sunlight and natural processes help reduce their levels, making the water safe again."
The council has carried out recreational water monitoring since 2006.
Warmer weather also brings toxic algae.
Toxic algae could occur in rivers and lakes throughout Otago. Blooms were more likely in summer when warm temperatures, low flows, plenty of sunlight, and the right nutrient conditions created an environment where they could grow quickly.
"Our monitoring is focused on popular recreation sites, but toxic algae can occur in many waterways across the region, so it’s important people know what to look for. Both Lawa and the ORC website are great places to learn," Ms Trotter said.
In lakes, toxic algae appeared as green "pea soup" or scum on the surface of the water.
In rivers, it was dark brown or black mats attached to rocks, often with a musty smell. These mats could detach and form floating rafts at the water’s edge or wash up on banks where risks to dogs and children were highest, she said.
Because blooms could develop quickly and not every site was monitored, the council encouraged people to be aware of toxic algae while at waterways.
Permanent signs are in place at some high-risk sites.
— Allied Media
