The Vasse-Wonnerup Estuary is an

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

in the

South West The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each se ...

region of

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...

close to the town of Busselton. The estuary is listed with DIWA. It was also recognised as a wetland of international importance under the

Ramsar Convention The Ramsar Convention on Wetlands of International Importance Especially as Waterfowl Habitat is an international treaty for the conservation and sustainable use of Ramsar site, Ramsar sites (wetlands). It is also known as the Convention on W ...

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.

Description

The estuary is wave dominated and has been severely modified from its natural state. The site of the Vasse and Wonnerup Floodgates 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 Samphire is a name given to a number of succulent salt-tolerant plants ( halophytes) that tend to be associated with water bodies. *Rock samphire, ''Crithmum maritimum'' is a coastal species with white flowers that grows in Ireland, the Uni ...

and rushes.

Paperbark ''Melaleuca'' () is a genus of nearly 300 species of plants in the myrtle family, Myrtaceae, commonly known as paperbarks, honey-myrtles or tea-trees (although the last name is also applied to species of ''Leptospermum''). They range in size f ...

woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ''plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (se ...

occurs behind the samphire belt, with

eucalypt Eucalypt is a descriptive name for woody plants with capsule fruiting bodies belonging to seven closely related genera (of the tribe Eucalypteae) found across Australasia: ''Eucalyptus'', ''Corymbia'', ''Angophora'', '' Stockwellia'', ''Allosyn ...

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,

Ludlow River The Ludlow River is a river in the South West region of Western Australia. It was named after Frank Ludlow, one of the first Western Australian colonists, an arrival on the barque ''Parmelia'' in 1829, who explored the locality in 1834. The h ...

, Sabina River and

Vasse River The Vasse River is a river in the South West of Western Australia. The headwaters of the river are in the Whicher Range below Chapman Hill and it flows in a northerly direction through the City of Busselton until discharging into the Vasse E ...

all discharge into the estuary. The catchment covers a total area of and is part of the

Geographe Bay Geographe Bay is in the south-west of Western Australia around 220 km southwest of Perth. The bay was named in May 1801 by French explorer Nicolas Baudin, after his ship, ''Géographe''. The bay is a wide curve of coastline extending from ...

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 Busselton 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 The black-winged stilt (''Himantopus himantopus'') is a widely distributed very long-legged wader in the avocet and stilt family ( Recurvirostridae). The scientific name ''H. himantopus'' is sometimes applied to a single, almost cosmopolitan sp ...

banded stilt The banded stilt (''Cladorhynchus leucocephalus'') is a nomadic wader of the stilt and avocet family, Recurvirostridae, native to Australia. It belongs to the monotypic genus ''Cladorhynchus''. It gets its name from the red-brown breast band fo ...

, Australasian shoveller,

Australian shelduck The Australian shelduck (''Tadorna tadornoides''), also known as the chestnut-breasted shelduck or mountain duck, is a shelduck, a group of large goose-like ducks part of the bird family Anatidae. The genus name ''Tadorna'' comes from Celtic root ...

and the

red-necked avocet The red-necked avocet (''Recurvirostra novaehollandiae'') also known as the Australian avocet, cobbler, cobbler's awl, and painted lady, is a wader of the family Recurvirostridae that is endemic to Australia and is fairly common and widespread t ...

. The largest breeding colony of black swans in Western Australia (over 150 pairs) is in the estuary.

Fish kills

Fish kills 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 Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

levels were to blame. Rainfall washed nutrients downstream to the estuary then a warm spell sparked the growth of algae 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