The Palmiet estuary was historically considered a permanently open system that only closed for a short period every few years, but the mean annual run-off has been reduced by an estimated 36% due to abstraction and impoundments (dams), and alien infestation in the catchment.
The resulting reduction in river flow and floods causes more frequent and longer duration mouth closure, as well as reduced scouring of accumulated sediment. Furthermore, the Palmiet River is a ‘black water’ system characterised by low inorganic nutrient concentrations, so the increased nutrient load from the catchment results in aquatic weed blooms in the estuary. As these blooms die and decay, bacterial decomposition processes deplete the oxygen concentration in the water, putting the rest of the ecosystem under stress.
Nevertheless, the estuary is in a good condition, and a recent Ecological Water Requirement study yielded a ‘recommended ecological category’ of B. Google Earth image