Dissolved oxygen levels in Macquarie Harbour continue to improve

Two EPA scientists have reviewed long term data sets to create a status update for dissolved oxygen in Macquarie Harbour. The report shows a clear trend of improving oxygen levels in the middle and deeper waters of the harbour. 

Each graph presented in the report is created from statistical analysis of hundreds of data points. Two independent data sets have been used, the monthly broadscale environmental monitoring program that salmon companies are required to undertake and the EPA's own quarterly monitoring program which has been ongoing since 1993. Both data sets show an overall improvement in dissolved oxygen levels that are now close to the range observed prior to 2010, when dissolved oxygen levels began to decline. 

Oxygen levels further from the harbour mouth remain further from the target range. 

The data used in the report does not include the major recharge event which occurred on 31 May 2024. Furthermore, the Macquarie Harbour Oxygenation Project has not yet reached its full scale and is unlikely to have yet had a significant impact upon oxygen levels across the harbour. As such we can expect to see further improvements because environmental licence conditions imposed by the EPA on salmon companies require them to either continue to operate oxygenation equipment after the trial concludes or to reduce their oxygen demand by other means, such as reducing biomass. 

The above is separate to another line of evidence showing improvement that was recently reported by the EPA. Seabed video surveys at 35m compliance points showed the best consecutive survey results seen since EPA became responsible for environmental regulation, see compliance history table

Commencing in 2017, the EPA Director progressively cut finfish farming in Macquarie Harbour by half. ​

 Macquarie Harbour - Status update for dissolved oxygen (PDF 1Mb)

Published on: 27/06/2024