The health warning issued for toxic algae in Lake Hood has been lifted, Health New Zealand announced today.

The warning, which was put in place on March 20, 2025, has been removed following recent water tests that show levels of potentially harmful blue-green algae (planktonic cyanobacteria) have dropped below the threshold of concern for public health.

Dr Ramon Pink, Medical Officer of Health for the National Public Health Service, confirmed that Environment Canterbury will continue to monitor the lake monthly.

“The public will be informed if testing shows that concentrations have increased and there is a risk to public health again,” Dr Pink said.

Blue-green algae occur naturally in lakes and rivers but can quickly multiply during warmer months due to nutrient levels and calm weather. While not always visible, algal blooms can cause health issues such as skin rashes, nausea, and numbness. Toxins may also remain in the water even after the bloom disappears.

Health officials continue to urge caution when swimming or using lakes and rivers, especially if the water appears cloudy, discoloured, or contains visible algae. Pets should also be kept away from affected water.

For more information on current health warnings and water quality updates, visit Environment Canterbury’s website.