An algal bloom in Doubtful Sound, that coincided with reports of unusual numbers of fish deaths, is not considered to be toxic.

On 10th January Environment Southland (ES) launched an investigation into the bloom after commerical operators reported higher than normal deaths of jack mackerel in the area.

ES has now confirmed that results from samples of phytoplankton taken at Crooked Arm, Doubtful Sound on 11 January suggest there is no human health risk related to the consumption of kai moana, nor recreational activities in the area.

According to the results, the blooming algae are from the Skeletenoma genus, a marine diatom not known to be toxic, they said.

Further test results suggest that Skeletenoma are also in higher than usual numbers along the open coast of Te Rua-o-te-moko Fiordland.

There was concern that fish deaths also reported in the area at the time were linked to the algal bloom.

However, due to the condition of the fish samples taken from the fish die off, the cause of death was unable to be determined and there have been no further reports of fish die offs to date.

ES will conduct ongoing monitoring of the bloom situation in coordination with partner agencies, tourism operators and the fishing industry, they said.