The Hay River is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in the Great Southern

Great Southern

Great Southern can refer to any of the following:*Great Southern Television, based in Auckland and Sydney.*Great Southern , a region in Western Australia.*Great Southern , the backing band for American rock guitarist Dickey Betts....

 region of Western Australia

Western Australia

Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

.

The river is part of the Denmark

Denmark, Western Australia

Denmark is a town in the Great Southern region of Western Australia, south-south-east of the state capital of Perth. At the 2006 census, Denmark had a population of 2,732.-History:...

 catchment along with the Denmark River

Denmark River

The Denmark River is located in the Great Southern region of Western Australia.The river rises near Pardelup and meanders in a southerly direction until it flows through Denmark into Wilson Inlet ....

 (West of the Hay River) and the Sleeman-Cuppup River (to the east of the Hay River).

The river rises West of Mount Barker

Mount Barker, Western Australia

Mount Barker is a town on the Albany Highway and is the administrative centre of the Shire of Plantagenet in the Great Southern region of Western Australia...

 near Wilpuna Park and flows south east as far as Ungerup then flows in a south south westerly direction through the Mount Lindesay National Park then crossing the South Coast Highway

South Coast Highway

South Coast Highway is a Western Australia highway. It is a part of the Highway 1 network.With a length of , it runs from Esperance to Walpole roughly in parallel to the Western Australia's south coast...

 and discharging into Wilson Inlet

Wilson Inlet

Wilson Inlet is an inlet located in the Great Southern region of Western Australia.The inlet receives water from the two main rivers: the Denmark River and the Hay River and some smaller rivers and streams such as the Sleeman River, Little River and Cuppup Creek...

.

The tidal influence is 5 kilometres (3 mi) upstream from where the river flows into the inlet.
The Hay river flows all year and the water quality

Water quality

Water quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...

 is marginally saline

Saline water

Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....

 to brackish. It is estimated that 70% of the catchment

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 area has been cleared for agricultural purposes but 42% of the riparian zone was pristine.

Tributaries

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

of the river include Sleeman Creek and Mitchell River.