The Vasse-Wonnerup Estuary is an estuary in the South West region of Western Australia close to the town of

Busselton Busselton is a city in the South West region of the state of Western Australia approximately south-west of Perth. Busselton has a long history as a popular holiday destination for Western Australians; however, the closure of the Busselton ...

. The estuary is listed with DIWA. It was also recognised as a wetland of international importance under the Ramsar Convention on 7 June 1990 when an area of was designated Ramsar Site 484 as an important dry-season habitat for waterbirds. It is also the main part of the Busselton Wetlands

Important Bird Area An Important Bird and Biodiversity Area (IBA) is an area identified using an internationally agreed set of criteria as being globally important for the conservation of bird populations. IBA was developed and sites are identified by BirdLife Int ...

Description

The estuary is wave dominated and has been severely modified from its natural state. The site of the

Vasse and Wonnerup Floodgates The Vasse and Wonnerup Floodgates is a heritage listed site in Western Australia that comprises two locations. The two locations are the site of the Vasse floodgates on the Vasse River and the Wonnerup floodgates on the Wonnerup Estuary. In addit ...

that regulated the flow of water in the estuary from about 1907 inadvertently created the freshwater wetland, were listed on the Western Australian Register of Heritage Places in 2005. The estuary covers a total surface area of with the central basin having an area of In winter, wide areas of open water are fringed by samphire and rushes. Paperbark woodland occurs behind the samphire belt, with eucalypt woodland on higher ground.

Catchment

The catchment of the estuary is 52% cleared and is used primarily for crops and pastures but also for plantations. The waters are susceptible to pollution from run-off as houses in Busselton have been built adjacent to the estuary. The

Abba River The Abba River is a river in the South West region of Western Australia. The headwaters of the river rise in the Whicher Range in the Millbrook State Forest then flow in a northerly direction. The river crosses the Vasse Highway and then thr ...

, Ludlow River,

Sabina River The Sabina River is a river in the South West of Western Australia. The headwaters of the river rise in the Whicher Range near the edge of the Millbrook State Forest and then flowing in the northerly direction. The river crosses the Vasse Hig ...

and Vasse River all discharge into the estuary. The catchment covers a total area of and is part of the Geographe Bay catchment. The coastal plain area is composed of sandy and duplex soils that are easily water-logged. An extensive drainage network has been constructed to protect

and Wonnerup from flooding and to create agricultural land.

Birds

It is estimated that over 20,000 waterbirds use the estuary as habitat with over 80 species of waterbird being found. Some of the species found in the area include black-winged stilt, banded stilt,

Australasian shoveller The Australasian shoveler (''Spatula rhynchotis'') is a species of dabbling duck in the genus ''Spatula''. It ranges from 46 to 53 cm. It lives in heavily vegetated swamps. In Australia it is protected under the National Parks and Wildli ...

, Australian shelduck and the red-necked avocet. The largest breeding colony of

black swan The black swan (''Cygnus atratus'') is a large waterbird, a species of swan which breeds mainly in the southeast and southwest regions of Australia. Within Australia, the black swan is nomadic, with erratic migration patterns dependent upon c ...

s in Western Australia (over 150 pairs) is in the estuary.

Fish kills

Fish kill The term fish kill, known also as fish die-off, refers to a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (2005) ''Plant Management in Fl ...

s have occurred in the estuary in 2009, 2011 and 2013. In the 2013 event an estimated 7,000 fish died over the course of two days, calling into question the health of the waterway. It is thought that low flows, poor water quality and high phosphorus levels were to blame. Rainfall washed nutrients downstream to the estuary then a warm spell sparked the growth of

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

depleting the water of oxygen, killing the fish.

References

{{coord, 33, 38, S, 115, 24, E, display=title, region:AU_type:waterbody_source:GNS-enwiki Estuaries of Western Australia Ramsar sites in Australia Swan Coastal Plain Important Bird Areas of Western Australia Busselton DIWA-listed wetlands