Warning: Toxic algae building up in district's streams and rivers

YUK: Low flows and algae infestation has brought on river warnings at Te Ore Ore, near Masterton.

Dry weather and low river flows have impacted on the Ruamahanga River with algae growth reaching such high levels that the Te Ore Ore section of the river has been declared unsafe for swimming and for dogs off leashes.

A toxic algae red alert has been issued by Greater Wellington Regional Council warning that the proliferation of "detached cyanobacteria "mats" accumulating on the river's edge makes the site unsafe.

At Kokotau, in rural Carterton, the toxic algae cover in the river is above the 20 per cent amber alert threshold meaning that while it is still safe to use the river, people should avoid touching the algae and must keep dogs on leads.

Warnings are also in place for Henley Lake in Masterton.

Masterton and Carterton district councils are posting toxic algae information signs at key access points along the rivers and information on coast and river water quality is on www.gw.govt.nz/summer-check

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 is 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 owners are warned to keep their dogs on a lead when near rivers.

Regional council senior environmental scientist Summer Greenfield said river conditions could change rapidly and as only certain points were monitored it is possible there are algae blooms happening at other spots.