A toxic algae invasion has prompted a warning for swimmers and dog owners to keep away from parts of the Hutt River.
Monitoring of the upper parts of the river has found a large amount of algae that is potentially lethal to dogs and livestock washing up.
Contact can also cause vomiting, diarrhoea and skin irritations in humans.
The Hutt City Council has asked people to now avoid swimming in the area or walking their dogs there.
"The downside of the great summer weather we've been having is that it creates ideal conditions for toxic algal growth in rivers," senior environmental scientist Summer Greenfield said.
"It's likely that toxic algae is present to some extent all along the Hutt River at the moment, so we encourage river users to find out what toxic algae looks like so they can avoid it."
Last week the death of a dog prompted a similar warning for the Otaki River.
NZN