28/04/2026
Summary of Dr Deb Geronimi’s report from Revive Lake Cathie’s latest water watch
Overall conclusion
The lake system was surprisingly good after its 5-month closure. Ammonia concentrations were low at all sites.
Oxygen concentrations were low to moderate for most sites. They were dangerously low for site 6 and no marine life was found at this site. Oxygen levels are therefore a concern.
The pH was in normal ranges for most sites. The lake system had brackish salinity readings which is expected as rainfall would have diluted the salt in the sea water since lake closure from the ocean.
Iron concentrations were low to moderate.
Concentrations of surfactants (detergents) were low to moderate and therefore not good for the lake system. Detergents get washed into the lake from the land, for example, when people wash their cars.
Tannins caused by the breakdown of plant leaves were moderate to high in concentration (which is quite normal).
In February 2026 RMS Lake Innes and Site 6 Lake Cathie had no marine life. Fish such as Pufferfish, Mullet, Fingerlings, Stingrays and Prawns were seen at many sites around Lake Cathie. Fishers have also been catching Flathead. Also clumps of Seagrass were found at many sites which is great news. Lots of bird life was present throughout the system.
It will be interesting to see what the next water watch results bring in May. There are concerns for aquatic life. The fact that Stingrays such as The Estuarine Stingray (Hemitrygon fluviorum), listed as Vulnerable on the IUCN Red List and other marine species are now trapped in the lake system and cannot escape to the ocean, is a huge concern. Currently the system has been diluted to brackish conditions from recent rainfall events. The last time the lake closed to the ocean several mass fish and Stingray mortality events occurred. Therefore, both rainfall events (freshwater conditions) and / or dry spells (drought and evaporation - could lead to hypersaline conditions) would be detrimental to our marine life in the lake.
