River health warnings
We monitor river sites regularly over the summer to check for bacteria (faecal contamination) and toxic algae.
Each river site is given a long-term grade prior to the summer monitoring season for suitability for swimming and recreation. The grade is based on the last five years of sampling. Sites that are not recommended for swimming because of their long-term grade are red on the Land Air Water Aotearoa (LAWA) website and signage should be in place at the site. Temporary Health warnings are issued when a site is graded as good to swim but there is now an increased risk of cyanobacteria or faecal contamination.
- Toxic algae (cyanobacteria) can occur in any waterway, at any time, so it is important that you know what it looks like. Find out more about toxic algae and how you can protect yourself and your animals.
- Faecal contamination poses a risk to health, it can cause gastrointestinal illnesses, respiratory diseases, and eye, ear, nose, throat and skin infections.
Temporary health warnings
Ashley River | Rakahuri at SH1
Health New Zealand has issued a health warning for Ashley River | Rakahuri at SH1.
The warning follows the finding of high levels of faecal bacteria in Ashley River | Rakahuri at SH1.
Water quality at affected sites is not considered suitable for recreational uses including swimming because of the risk to health from the bacteria and other pathogens.
Find out more: Land, Air, Water Aotearoa (LAWA) - Ashley River | Rakahuri at SH1
Waihi River at Waihi Gorge
Health New Zealand has issued a health warning for Waihi River at Waihi Gorge.
The warning follows finding moderate to high cover of potentially toxic harmful algae (benthic cyanobacteria) in the Waihi River at Waihi Gorge.
People should avoid the area and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.
There are also other access points along the Waihi River at Waihi Gorge 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.
Find out more: Land, Air, Water Aotearoa (LAWA) - Waihi River at Waihi Gorge
Waihao River at Gum Tree Flat Road
Health New Zealand has issued a health warning for Waihao River at Gum Tree Flat Road (Don's Hole).
The warning follows findings of high levels of faecal bacteria in consecutive samples taken from Waihao River at Gum Tree Flat Road (Don’s Hole).
An existing health warning at Waihao River at Gum Tree Flat Road (Don’s Hole) remains in place for harmful algal bloom (benthic cyanobacteria). This warning was issued on 21 November 2025.
Find out more: Land, Air, Water Aotearoa (LAWA) - Waihao River at Gum Tree Flat Road
South Bank Tributary of the Waiau Uwha River above Waiau Bridge
Health warning
Health New Zealand has issued a health warning for the South Bank Tributary of Waiau Uwha River above Waiau Bridge.
The warning follows finding moderate to high cover of potentially toxic harmful algae (benthic cyanobacteria) in the South Bank Tributary of the Waiau Uwha River above Waiau Bridge.
People should avoid the area and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.
There are also other access points along the South Bank Tributary of the Waiau Uwha River above Waiau Bridge 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.
Find out more: Land, Air, Water Aotearoa (LAWA) - South Bank Tributary of the Waiau Uwha River
Selwyn River at Glentunnel and Whitecliffs
Health New Zealand has issued a health warning for Selwyn River at both Glentunnel and Whitecliffs.
The warning follows finding moderate cover of potentially toxic algae (benthic cyanobacteria) in the Selwyn River.
People should avoid the area and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.
Find out more: Land, Air, Water Aotearoa (LAWA) - Selwyn River at Glentunnel and Land, Air, Water Aotearoa (LAWA) - Selwyn River at Whitecliffs
Pareora River at Pareora Huts
Health New Zealand has issued a health warning for the Pareora River at Pareora Huts.
The warning follows finding moderate to high cover of potentially toxic harmful algae (benthic cyanobacteria) in the Pareora River at Pareora Huts.
People should avoid the area and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.
Find out more: Land, Air, Water Aotearoa (LAWA) - Pareora River
Waihao River at Gum Tree Flat Road
Health New Zealand has issued a health warning for Waihao River at Gum Tree Flat Road (Don's Hole).
The warning follows finding moderate to high cover of potentially toxic harmful algae (benthic cyanobacteria) in the Waihao River at Gum Tree Flat Road (Don's Hole).
People should avoid the area and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.
There are also other access points along the Waihao River at Gum Tree Flat Road 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.
Find out more: Land, Air, Water Aotearoa (LAWA) - Waihao River at Gum Tree Flat Road
