A once popular swimming river in Canterbury is barely flowing in parts and poisoned by toxic algae.
Locals said the condition of the Selwyn River was the worst it had been and its condition had ruined summer.
One said it was in such a poor state, he would neither swim in it nor eat fish from it.
The algae - benthic cyanobacteria - looked like dark brown to black mats, and could produce toxins that were harmful to people and animals, the health board said.
Irrigation restrictions were in place on parts of the river.
Environment Canterbury (ECan) recently gave its water quality the lowest possible rating.
Local resident and river campaigner Matt Olykan said the river quality had declined, particularly in the past few years.
He said the flow was poor and the river was virtually at a standstill at this time of year, particularly near the Selwyn Huts.
Mr Olykan said the gunge in the water was thick and the summer on the river was ruined.
Local dairy farmer and ECan councillor John Sunckell said the issue was complicated.
The Selwyn River was in a state of disrepair, but a lot of work was going into its remediation, he said.
The catchment was over-allocated for irrigation, he said, and the community was starting to see the combined effects of three years of drought and poor management.
Last year, ECan revealed the number of Canterbury waterways that were safe to swim in had decreased from 74 per cent in 2010 to 67 per cent.