Residents of Taranaki are advised to exercise caution around waterways due to the discovery of harmful cyanobacteria earlier in the season than usual. Four rivers; the Manganui, Waingongoro, Kaupokonui, and Waiwhakaiho Rivers have revealed cyanobacteria mats, according to the Taranaki Regional Council, causing health risks for swimmers and pets. As summer approaches in New Zealand, the Taranaki Regional Council summed up efforts to ensure safe recreational water use with its monitoring programme, titled Can I Swim Here?, which tested water quality at 41 popular spots from November 2023 to March 2024.
Council Water Quality Scientist Angela Collins states:
“Children are at greater risk because their smaller body size means they need to ingest less toxin to become seriously ill, while dogs may be attracted to the musty smell.”
So, when these mats are present, the safest course of action is to avoid entering the water altogether and ensure that children and pets are closely supervised to prevent accidental contact or ingestion.
Source credit: RNZ (An example of algae clogging a river)
Not new for the Taranaki residents
Cyanobacteria mats have been a recurring problem in Taranaki. Past incidents highlight the increasing prevalence of algal blooms in the region:
2019: Coastal Taranaki residents, including surfers and local hapū (Māori sub-tribes), raised concerns about algal blooms clogging rivers. These blooms disrupted traditional food gathering and were linked to nutrient runoff from nearby farms.
2020:A dog died after ingesting toxic algae from the Wairarapa River, underscoring the importance of recognizing and avoiding hazardous water conditions.
2023: A dense blue-green algae bloom triggered health warnings at Lake Ngangana in Waitara. Signs advised the public to avoid contact with the water.
Cell counts and biovolume measurements are utilized to assess risk levels. These thresholds provide a systematic method for quantifying cyanobacteria concentrations and evaluating potential health risks:
Source: trc.gov.nz
Low Risk: Fewer than 2,000 cells per milliliter or a biovolume of less than 0.5 mm³/L.
Medium Risk: Between 2,000 and 15,000 cells per milliliter, or a biovolume of 0.5–1.8 mm³/L.
High Risk: More than 15,000 cells per milliliter or a biovolume exceeding 1.8 mm³/L.
A new way of measuring cyanobacteria levels was introduced in 2014-2015. Along with simply looking at the cyanobacteria (visual checks), scientists started measuring the amount (biovolume) of cyanobacteria in the water. By using both methods together, the Taranaki Regional Council (TRC) can now more accurately detect and manage the risks that cyanobacteria pose to people and animals in rivers.
Whats next?
The TRC continues its summer awareness campaign to inform residents about safe water use. People can check water quality reports and health advisories on the council’s website or social media.
Abby Mathews, the council’s environmental quality director, explains that heavy rain often carries fecal matter into rivers. She advises residents to avoid water for at least three days after rainfall.
“When it rains, fecal matter is carried into rivers, posing health risks to anyone who comes into contact with the water.”
Mathews advised people to avoid water for at least three days after heavy rainfall as well as mentioned that the council would continue its summer awareness campaign to help people make informed choices.
Monitoring and controlling algal blooms
One of the most effective approaches to managing water quality involves early detection and monitoring, which are critical in controlling algal blooms and maintaining healthy aquatic systems. Advanced systems that combine real-time data collection with cloud-based analysis provide an efficient solution for water management, enabling early warnings of cyanobacteria increases.
Community involvement
Additionally, community involvement will play a key role in shaping the Land and Freshwater Plan by TRC. Public consultations aim to balance environmental protection with the region’s agricultural and recreational needs. This collaborative approach ensures that diverse perspectives are considered, creating sustainable water management practices that benefit both the community and the environment.
