Horizons Regional Council's summer swim spot monitoring programme is under way to help inform the public about potential health risks.
The annual monitoring programme runs from November to the end of April and tests bacteria levels for freshwater rivers and lakes, and coastal beaches.
Some freshwater sites are also regularly monitored for potentially toxic algae.
Horizons collects, analyses and reports on swim spot monitoring over summer through the Can I Swim Here? module on the Land, Air, Water Aotearoa (Lawa) website to help the public decide when and where they can swim over summer.
"Weekly water samples collected from each site are sent to an independent accredited lab for testing," Horizons natural resources and partnerships group manager Dr Jon Roygard says.