Lagoon water quality improves

The Waituna Lagoon has taken a turn for the better.

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

"Visual observations at the time of sampling by experienced technical staff showed discolouration had reduced which indicates decreased algal levels," Environment Southland integrated catchment management general manager Paul Hulse said.

The available data shows that, as at February 8, 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 has decreased to around mid-2023 levels.

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

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

On February 16, a probe was installed at the centre monitoring platform in the lagoon, to obtain continuous monitoring data for various nutrients. No data is available from the probe at present. 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," Mr Hulse said.