![\"One](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/01\/4JUHNBO_e7e30591e4c61ec0aab772d5d3449b4df8a9be9b_4032x3024_webp.jpeg\")
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\nOne of the popular Wairarapa swimming spots along the Ruamahanga River, between Double Bridges and the Waingawa River.
\nPhoto: Supplied\/LDR\n<\/p>\n
An expert is warning Wairarapa swimmers about risks caused by contamination of the region’s rivers.<\/p>\n
Greater Wellington Regional Council senior environment adviser Penny Fairbrother says, while toxic algae in the rivers is currently at low levels, other risks remain.<\/p>\n
“We monitor numerous spots on Wairarapa rivers,” Fairbrother said. “At present, the vast majority of sites are showing it’s not suitable for swimming.”<\/p>\n
While algal bloom was unusually low for this time of year, there was no room for complacency, she warned.<\/p>\n
“Rivers can be contaminated with high levels of bacteria, mostly as a result of heavy rainfall.<\/p>\n
“That’s as a result of high rainfall washing contaminants into the river making it unsuitable for swimming.”<\/p>\n
<\/p>\n
Bacteria in rivers could cause infections like gastroenteritis, which make swimming dangerous.<\/p>\n
She said four of Wairarapa’s five rivers were at either red or orange levels for bacteria – the Ruamahanga, Waiohine, Waingawa and Waipoua. Only the Tauherenikau River was safe for swimming.<\/p>\n
The ‘golden rule’<\/p>\n
“The rivers should clear back to green level within 48 hours, depending on rainfall levels,” said Fairbrother. “The golden rule is not to swim for two days after heavy rain.”<\/p>\n
A green level indicated it was safe for swimmers and pets.<\/p>\n
Fairbrother said rain could be a double-edged sword – too much rain risked elevating bacteria levels, while too little meant conditions became ripe for toxic algae to bloom.<\/p>\n
There was a ‘Goldilocks’ period between heavy rainfall and very low rainfall levels.<\/p>\n
“Ideal conditions for toxic algae are warm weather, stable river flows, and no or little rain. Once we have a decent rainfall, it has a scouring effect, which washes the algae off the rocks.<\/p>\n
“It’s almost like a washing machine effect.”<\/p>\n
She said, once the algae washed down the river and reached the sea, it couldn’t survive.<\/p>\n
“Beautiful warm dry periods allow the algae to flourish.”<\/p>\n
She said, until recently, Wairarapa rivers had toxic algal bloom at low levels, but that had changed at two sites.<\/p>\n
Last week, the Waipoua River at Colombo Rd and the Ruamahanga River at Te Ore Ore were both at amber levels for algae.<\/p>\n
“That indicates the presence of moderate levels of algae.”<\/p>\n
An amber alert indicated relatively low risk for dogs and swimmers.<\/p>\n
“As a rule of thumb, dogs should never be allowed to scavenge from the river bank,” Fairbrother said. “While the risk remains low at this level, people should exercise caution.”<\/p>\n
Danger for dogs and swimmers<\/p>\n
There had been no algae red level in Wairarapa this year so far.<\/p>\n
That alert level would mean more than 50 percent of the river was covered in black mats or there were detached mats.<\/p>\n
Detached mats were big patches of bloom, which could float to the river’s edge.<\/p>\n
“That’s when it becomes really dangerous for dogs,” she said. “Dogs really love the smell and will eat the mats.<\/p>\n
“It’s highly poisonous for dogs. It releases a neurotoxin, and dogs and other mammals are highly susceptible to that.”<\/p>\n
Fairbrother said an algal mat the size of a 50-cent coin could kill a dog, if ingested.<\/p>\n
“We are also really worried about young children, who could put it in their mouths.”<\/p>\n
She said there had been signs of algae early this season, but regular bouts of rain had made the difference and kept the risk low.<\/p>\n
Do not relax<\/p>\n
It was still too early to predict what could happen for the rest of the season.<\/p>\n
“Do not relax,” she warned. “If we get 2-3 weeks of amazing weather in February or March, there is every possibility of a big algal bloom.<\/p>\n
“We monitor right through until April.”<\/p>\n
LDR is local body journalism co-funded by RNZ and NZ On Air<\/p>\n","protected":false},"excerpt":{"rendered":"One of the popular Wairarapa swimming spots along the Ruamahanga River, between Double Bridges and the Waingawa River.…\n","protected":false},"author":2,"featured_media":242368,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[48,47,111,43,139,69,49,46,44,45],"class_list":{"0":"post-242367","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-new-zealand","8":"tag-audio","9":"tag-current-affairs","10":"tag-new-zealand","11":"tag-news","12":"tag-newzealand","13":"tag-nz","14":"tag-podcasts","15":"tag-public-radio","16":"tag-radio-new-zealand","17":"tag-rnz"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/242367","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=242367"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/242367\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/242368"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=242367"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=242367"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=242367"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}