Water samples taken from the Waituna Lagoon following its opening to the sea on 31 January show water clarity has improved across all four long-term monitoring sites to within normal range, while salinity and conductivity have increased, according to Environment Southland (ES). 

ES General Manager Integrated Catchment Management Paul Hulse said visual observations at the time of sampling by experienced technical staff showed discolouration had reduced which indicates decreased algal levels.  

The available data shows that, as at 8 February, opening the lagoon had worked to reduce algae back to mid-2023 levels.

However, the algae present were still dominated by potentially toxin-producing species.

Cynobacteria remains in some areas of the lagoon, so the public health alert remains in place. 

Nutrient levels are still high, but chlorophyll-α has decreased to levels around that seen in mid-2023.

Sampling following the opening has occurred on the 1, 8, 16 and 22 February, with laboratory results only partially available.  

Monitoring is continuing to occur weekly with a full suite of sampling sites being tested fortnightly.  

On 16 February, a probe was installed at the centre monitoring platform in the lagoon, to obtain continuous monitoring data for various nutrients.

ES advised no data is currently available from the probe, it will be downloaded when the next full suite of samples are obtained.

“It is interesting to note conditions deteriorated markedly in the days leading up to the lagoon being opened, further supporting the decision to open,” Hulse said.