Toxic algae alerts for Hutt and Ruamāhanga Rivers

  • Published Date 28 Jan 2015

Toxic algae warnings have been put in place on parts of the Hutt and Ruamāhanga Rivers.

Red alert toxic algae warnings are in place for the Hutt River at Poets Park, Silverstream and Boulcott.  Large amounts of detached cyanobacteria mats have been recorded at monitoring sites in these areas meaning that it is unsafe for swimming.  Dogs should be kept away from these parts of the river.

The Ruamāhanga River at Te Ore Ore has large amounts of detached cyanobacteria mats accumulating on the river's edge making this site unsafe for swimming and unleashed dogs.  At Kokotau the cover of toxic algae in the river is above the 20% amber alert threshold meaning that while it's still safe to use the river, people should avoid touching the algae and keep their dog on a lead.

Warnings are also in place for Henley Lake in Masterton and Whitby Lake in Porirua.

Hutt and Upper Hutt City Councils and Masterton and Carterton District Councils are posting toxic algae information signs at key access points along these rivers and the latest information on coast and river water quality is on

Hot, dry conditions over the last few weeks mean that river conditions are ideal for the growth of algae including cyanobacteria.  The brown or black toxic algae are visible as mats on the river beds. These can wash off and build up on the river's edge. If ingested the algae can kill livestock and dogs and contact can cause vomiting, diarrhoea and skin irritations in humans.

Some dogs have a tendency to eat the algae so dog owners are warned to keep their dogs on the lead when near rivers.

"River conditions can change rapidly and as we only monitor at certain points it is possible there are blooms occurring at other locations. River users are advised to scan for toxic algae before going in the water or letting dogs off their leads," says Regional Council Senior Environmental Scientist Summer Greenfield.

Monitoring of Wellington waterways and coastal areas is carried out by Greater Wellington Regional Council, local authorities and Regional Public Health on a weekly basis over the summer months. Results of the monitoring and other information is posted

Updated April 29, 2022 at 11:40 AM

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