Dangerous levels of toxic algae have been found in parts of the Hutt River.
It's prompted a plea from local council urging people not to swim in the area or let their dogs into the water - and the issue isn't going away anytime soon.
The Hutt River is a popular spot for dog owners and swimmers but now the Greater Wellington Regional Council is strongly warning people to avoid the water.
"There are very high levels of toxic algae, and so we've advised people not to swim or bring your dog off-leash," a spokesperson told Newshub.
Toxic algae is growing rapidly in the Hutt River. It's a dark colour and grows on rocks and while it might not look like much of a threat, it's dangerous.
"Dogs who are off leash come along and find it, and apparently it smells delicious to dogs, so dogs will eat it, get sick and often die. It's also very poisonous to humans," the council spokesperson said.
A red swimming alert is now in place from Maoribank right through to Taita Rock.
"The best advice is for people to be vigilant and learn what toxic algae looks like, whether it's in the river or detached on mats by the river," the council spokesperson said.
People who've been in contact with toxic algae and are feeling unwell are being advised to seek urgent medical attention.
If your dog has swallowed some, you should take it to the nearest vet immediately.
"When we've got very warm weather and very little rain, it grows really fast," freshwater scientist Dr Susie Wood said.
Dr Wood is an expert on toxic algae and said one of the leading causes of this is warmer temperatures.
"It's likely that we will see more problems in the years ahead, as we get these longer, warmer periods, with less rainfall," Dr Wood said.
So be prepared Wellingtonians for more red alerts and less swimming in the future.
