The Hamersley River is an ephemeral

Ephemeral

Ephemeral things are transitory, existing only briefly. Typically the term is used to describe objects found in nature, although it can describe a wide range of things....

 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 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 headwaters of the river rise east of Fitzgerald and just north of 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...

 on an undulating sandplain on the edge of the Yilgarn plateau and flows in a south easterly direction. The river flows through the Fitzgerald River National Park

Fitzgerald River National Park

Fitzgerald River National Park is a national park in Western Australia , southeast of Perth, in the Shire of Ravensthorpe and the Shire of Jerramungup....

 winding through gorges cut into faults in the quartzite

Quartzite

Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...

 and schist

Schist

The schists constitute a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. Quartz often occurs in drawn-out grains to such an extent that a particular form called quartz schist is...

 of the Mount Barren formation until discharging into the Hamersley Inlet and on to the Southern Ocean

Southern Ocean

The Southern Ocean comprises the southernmost waters of the World Ocean, generally taken to be south of 60°S latitude and encircling Antarctica. It is usually regarded as the fourth-largest of the five principal oceanic divisions...

.

Hamersley inlet is a wave dominated estuary

Estuary

An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

 is approximately 7 kilometres (4 mi) in length with a depth of about 2 metres (7 ft) with a total surface area of 2.9 square kilometres (1 sq mi).

The river was named by the explorer and surveyor

Surveying

See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...

 John Forrest

John Forrest

Sir John Forrest GCMG was an Australian explorer, the first Premier of Western Australia and a cabinet minister in Australia's first federal parliament....

 in 1871 while on expedition in the area. He is thought to have named it after his future wife, Margaret Hamersley

Margaret Forrest

Lady Forrest , born Margaret Elvire Hamersley, was the wife of Sir John Forrest. Born in Le Havre, France, she was a member of the prominent and wealthy Hamersley family; her father was Edward Hamersley , and amongst her brothers were Edward Hamersley and Samuel Hamersley...

 or her family

Hamersley family

The Hamersley family were a wealthy and well-connected family of early settlers in the colony of Western Australia. Members of the Hamersley family emigrated to Western Australia from England in 1837.Prominent members and connections of the family include:...

The river is an important drainage network in the National Park. The river flows very little under normal conditions but flood

Flood

A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

s infrequently after heavy rain events.

The upper part of the catchment has been mostly cleared for agriculture

Agriculture

Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...

but the lower part in the National park is in near prisitne condition. Overal 20% of the rivers catchment has been cleared.