Due to Sunday's heavy rainfall, the Hawke's Bay Regional Council's water quality testing has put most swimming sites in the red zone for bacteria levels.
The weekly testing takes place on Mondays, and although several days have since passed, swimmers and recreational water users are being told to use caution before swimming.
Rainfall often washes pollution and farming effluent into rivers, which raises their fecal contamination levels, and it's recommended people wait three days before swimming.
Regional council coastal scientist Oliver Wade said if the public needed information about specific spots they could call the council or check its website.
"We got our results back today and the majority of them will be red," he said. "That basically holds the latest information about the water quality of the sites we normally sample."
However with the sites tested each Monday, immediate information might not be available so he suggested users not swim within three days of rainfall, and ensure water was running clear before entering.
"Because it's just weekly it's just a guideline. We can say 'we didn't get any exceedence on that day' but it doesn't mean things haven't changed."
Of the 32 sites tested, only the Clive River and the Puhokio Stream at Waimarama had permanent signposts warning of the water quality.
Regional council Water Quality and Ecology principal scientist Adam Uytendaal said although the rainfall had cleared the rivers of algae, bacteria levels may have risen. "The general advice is if the river is running dirty, then you're best to wait until it clears up," he said.
People can call 0800 B4U Swim or visit the HBRC's website for further information.