Environment Southland has issued a red alert for the Waiau River at Tuatapere because of the amount of a toxic algae in it.
Wairaurahiri Jet owner Joyce Kolk, who last week called the river an "unmitigated environmental disaster", received an email from Environment Southland on Thursday night, which says "the toxic algae cover is now within the Action (red mode) alert level."
The email says "Observations from Monday (Jan 14th) have continued to find elevated levels of toxic algae (cyanobacteria, phormidium sp.) in the Waiau River at Tuatapere. The wadeable reach average cover was 51 per cent. The toxic algae cover is now within the Action (red mode) alert level."
Joyce Kolk of Wairaurahiri Jet in Southland received a red alert about the amount of toxic algae in the Waiau River.
"Users should be vigilant and avoid contact with this algae.
"Similar growth is likely to be occurring in other places along the Waiau, its tributaries, and potentially other rivers in the region.
"Keep dogs on lead and children away from affected areas."
Environment Southland has not issued a warning about the upgraded red alert on its social media pages, but on its website it has a toxic algae alert for the Waiau River at Tuatapere, and there is also a warning on the Beacon website and the Land, Air and Water Aoteatoa [LAWA] website.
Ecosystem response Nick Ward said the council issued a toxic algae alert for the river at Tuatapere on December 19 and from its most recent assessment of this site this week, the alert remains.
"The December assessment found enough toxic algae in the river to require an alert, and the recent assessment has found an increase, therefore the advice to the public remains the same.
"We can't monitor every waterway all the time, so even if no warnings are in place for a river or lake, you should still look carefully for any signs of toxic algae before entering the water.
He said if the public had concerns that a river or lake may have toxic algae, they could report it to Environment Southland immediately.