This Waterwatch report records sudden changes in water parameters in Lake Cootharaba in the recent period November 2022 to March 2023.
During November all pH and Turbidity readings were around normal, while salinity was lower than usual following heavy rain earlier.
In December the Turbidity had risen significantly at Boreen Point and mid-lake, but this sudden sedimentation had not spread to Kinaba or Cooloothin. Weather conditions at that time were very windy , and we attribute the increased Turbidity to typical wind and wave action stirring up the shallow lake, Thereafter Turbidity at all sites quickly returned to normal levels
In January we suddenly obtained unexpectedly high alkalinity in the lake, with pH rising to an extreme of 10.4 at Boreen Point and 9.8 in Cooloothin Creek. This alkalinity was spreading into mid-lake, and in February the lower and western sides of the lake all recorded high pH values between 9.6 and 9.8. The alkalinity spread only slightly upstream, as pH at Kinaba remained normal. By late March all sites had returned to normal pH values. The alkaline water drained away slowly into the lower river giving a slightly high pH reading at Tronsons Drain of 8.8.
| PH Test Results | Location | 18/11/2022 | 19/12/2022 | 27/01/2023 | 28/02/2023 | 29/03/2023 |
|---|---|---|---|---|---|---|
| KIN 997 | Kinaba | 6.54 | 6.26 | 6.84 | 7.43 | 6.78 |
| COT 200 | Boreen Point | 7.20 | 7.46 | 10.42 | 9.65 | 7.70 |
| COT 205 | Mid Lake | 6.70 | 7.02 | 8.77 | 9.89 | 7.59 |
| COO 050 | Cooloothin | 6.52 | 7.88 | 9.80 | 9.61 | 7.57 |
| NOO 401 | Tronsons | 7.60 | 8.16 | 7.35 | – | 8.83 |
| LAKE AVERAGE | 7.30 |
We deduce that some alkaline material must have been dumped into the lake somewhere along the western shore between Kinaba and Cooloothin Creek, as it clearly spread from the lake edge somewhere south of Kinaba to mid-lake over a two month period. Unfortunately we cannot more precisely determine the source.
RECOMMENDATIONS
In the event of future similar occurrences:
Additional tests around the area should be implemented immediately to determine the spatial distribution and the chemical nature of the pollution and its possible source.
Additional tests should be made to monitor changes with time and Noosa Shire Council should be quickly involved to investigate the nature of the pollution.
B. McConkey, April 2023