Water Minister Dave Kelly today released the Oyster Harbour (Miaritch): Condition of the estuary 2016-19 report on three years of water quality monitoring.
The report summarises the main drivers of estuary health (flow and catchment condition), and the response of the estuary in terms of water quality and seagrass habitat.
Located in the State's Great Southern region, Oyster Harbour is also known as Miaritch in Menang Noongar language. Covering an area of 15.6 square kilometres, Oyster Harbour is permanently open to King George Sound and is the only south-coast estuary without a sand bar.
Two major rivers (the Kalgan and King) flow into the northern harbour and are estuarine (that is, influenced by tidal marine exchange) for approximately nine and seven kilometres respectively.
Water quality and seagrass cover in Oyster Harbour declined in the late 1970s and 1980s due to catchment clearing and excessive nutrient inputs. Seagrass has recovered remarkably well in the past 20 years because of improved catchment management activities and significant seagrass transplanting, leading to better water quality.
Today, Oyster Harbour generally has very good water quality. It is free from nuisance microalgal blooms, fish kills and concentrations of low oxygen, and is a success story of improved water quality in an estuarine environment.
However, occasional elevated levels of nutrients and evidence of microalgal activity in the northern section of Oyster Harbour has increased in recent years, especially in summer and autumn. Relatively high phosphate concentrations from the King River catchment may be a key contributor to this.
The Report recommends management should continue to focus on building resilience and adaptability where possible. The report can be found here.
As part of the McGowan Government's $25 million investment in the Healthy Estuaries WA program, $7 million has been allocated over four years to help improve water quality and restore the values of three south coast estuaries - Oyster Harbour, Wilson Inlet and Torbay.
As a partner of the Healthy Estuaries WA program, the Oyster Harbour Catchment Group has received $904,000 in program funding and assistance from the Department of Water and Environmental Regulation (DWER) and the Department of Primary Industries and Regional Development, to support increased water quality monitoring and ongoing works to reduce the nutrient runoff from farms into Oyster Harbour.
DWER also supports the Oyster Harbour Catchment Group in its ecosystem activities, such as restoring seagrass and native oyster reefs.
In 2018, the McGowan Government invested $1 million in a project to restore native oyster reefs in Albany's Oyster Harbour to progress on an election commitment to help improve recfishing, biodiversity and water quality in Oyster Harbour.
As stated by Water Minister Dave Kelly:
"Although the water quality in Oyster Harbour is currently very good, the ongoing impacts of climate change may pose a threat to this in the future.
"Significant reductions in rainfall in the State's south have seen reductions in freshwater flows and increased salinity in south coast estuaries.
"A changing climate is also resulting in more sporadic, atypical rainfall events which have the potential to deliver nutrient loads at times of high algal growth activity, in summer for example.
"This means the ongoing efforts to reduce the runoff of excess nutrients from the catchment are as important as ever.
"By working with farmers, landholders, industry, local government and catchment groups, the Healthy Estuaries WA program is supporting the effective monitoring and management of our important south-coast waterways, and reducing nutrient inputs from catchments."
