The Macquarie Marshes are a large inland wetland in northern New South Wales, Australia, formed where the Macquarie River, north of the town of Warren, loses its channel and spreads across flat plains before draining to the Darling River through the lower Barwon. They are not a fixed lake but a system of channels, reed beds, river red gum forest and floodplain whose size depends on the year’s flood: the largest recorded inundation, in the mid-1950s, covered about 4,780 km², and BirdLife International maps a 2,378 km² Important Bird Area from the extent of the 1990 flood. The core, about 100 km north of Warren, is protected as the Macquarie Marshes Nature Reserve, about 19,800 ha made up of the North and South Marsh reserves and a third small reserve; the North and South Marsh were listed as a Ramsar wetland of international importance on 1 August 1986. To see why a river ends in a marsh hundreds of kilometres from the sea, the story has to start in the rocks of its headwaters and work forward in time.
The Lachlan Fold Belt and Mount Canobolas: the uplands that feed the marshes
The water that reaches the marshes is collected on ancient country. The upper Macquarie catchment, around Oberon, Bathurst and Orange, sits on the Lachlan Fold Belt, a band of folded and faulted rocks formed between about 450 and 340 million years ago in the Middle Palaeozoic. Its rock beds are folded into chevron folds and cut by thrust faults, and the belt was once two to three times its present width of about 1,000 km before folding and thrusting squeezed it. That belt now underlies most of New South Wales and Victoria, and in the north-west of New South Wales it disappears beneath younger basin sediments, including those of the Great Artesian Basin.
The high ground on top of it is the Great Dividing Range, which forms the eastern edge of the Macquarie catchment from near Oberon in the south to Coolah in the north. The range is dated to the Carboniferous period, more than 300 million years ago, followed by a very long history of erosion. That erosion is why the range here is a tableland rather than a wall of peaks: the Bathurst Plains are undulating country at about 700 m, ringed by higher tablelands, and the Hill End plateau drained by the Turon River stands at about 1,100 m in the south.
A much younger event added the highest point of the Orange plateau. Mount Canobolas, 13 km south-west of Orange, is an extinct shield volcano that erupted in several phases between about 13 and 11 million years ago, building a peak of 1,397 m. It stands on a plateau with a general elevation of about 900 m, where the Bell River rises before joining the Macquarie in the stretch between Wellington and Dubbo. More important for the marshes than any single peak is where the rain falls: the peaks and tablelands of the catchment receive between 750 and 900 mm a year, spread fairly evenly through the seasons, while the plains where the marshes lie receive only 300 to 400 mm. The marshes depend on water that falls far upstream.
From White Rock to Warren: 960 km and a 517-metre fall
The Macquarie itself, known to the Wiradjuri as Wambuul, meaning winding river, begins below White Rock near Bathurst at about 671 m, where the Fish River (flowing through Oberon Dam) and the Campbells River (flowing out of Chifley Dam) meet. Wambuul became an official dual name in December 2021. From there the river runs generally north-west for about 960 km and falls only about 517 m over that whole length, a gradient that becomes almost imperceptible on the plains.
The descent happens in stages. Through the Bathurst Plains and past the Hill End plateau, the river is still in hill country, joined from the east by the Turon. At Burrendong, upstream of Wellington, it takes in the Cudgegong River from the hills around Rylstone. Between Wellington and Dubbo the land flattens, the Bell and Little rivers join, and north of Dubbo the Talbragar, the most important downstream tributary, comes in from the junction of the Great Dividing Range and the Liverpool Range. In all, the catchment covers more than 74,000 km², and over 72% of it is flat.
Below Dubbo the Macquarie flows north-west across open plains past Narromine and Warren, a town of 1,365 people at the 2021 census, 120 km north-west of Dubbo. Here the river begins to behave like the lower course of a delta, though it is nowhere near the sea. A complex network of effluent creeks, channels that carry water out of the river rather than into it, links the Macquarie with the Bogan and Darling systems. The river is losing energy and water at the same time: evaporation, under 1,000 mm a year south-east of Bathurst, rises to more than 2,000 mm a year by Bourke, far more than the plains receive as rain.
A river in that position cannot keep a single channel. With almost no slope to drive it, floodwater that arrives from the tablelands spills over its banks, drops its load of silt and clay, and spreads sideways. Repeated over thousands of floods, spills of this kind leave a flat country of channels, backswamps and floodplain rather than a valley. The Macquarie Marshes are the wet heart of that plain, and their extent each year is a measure of how much water the uplands have sent down.
Oxley’s ocean of reeds, 1818: where the channel gives out
The first European description of the marshes came from the explorer John Oxley, who followed the Macquarie downstream in 1818 hoping it would lead to an inland sea. He camped on the site of present-day Warren and pushed on by boat. Beyond the last trees the channel ran through reeds one to three feet deep, then, without any warning change in its width or speed, spread out from north-west to north-east among what he called an ocean of reeds. There was no channel left to follow. Oxley turned back, convinced he was on the margin of a shallow inland lake slowly filling with sediment washed down from the highlands.
He was wrong about the sea but right about the process. In 1828 Charles Sturt was sent to follow the Macquarie further to establish where it went. He worked through the marshes, which were later named after Governor Lachlan Macquarie as the river had been, and became the first European to reach the Darling River, which he named after Governor Ralph Darling. The water Oxley watched vanish into the reeds was not lost; in big floods it flows on past the marshes into the Barwon–Darling system upstream of Brewarrina.
What the floods built is a mosaic sorted by how often each patch gets wet. The most frequently flooded ground, now largely within the nature reserve, carries extensive beds of common reed, meadows of water couch, and forest and woodland of river red gum. Most of the wider area covered by the marshes in a large flood is used as rangeland or pasture. This is also Aboriginal country: the Wayilwan, a Ngiyambaa-speaking people, held land along the Macquarie and Marthaguy and down the Castlereagh, with their southern frontier near Quambone.
When the floods come, birds follow. More than 200 species have been recorded, and the reserve is one of the most important breeding sites in Australia for intermediate egrets and straw-necked ibis. The marshes have supported more than 1% of the world population of the endangered Australasian bittern, along with white-necked herons, nankeen night-herons, Australian white ibis, royal spoonbills and glossy ibis. The marshes also support at least 56 reptile species and 15 frog species.
Burrendong Dam and the shrinking floods since the 1950s
The youngest layer in the marshes’ history is human engineering. The idea of damming the Macquarie upstream of Wellington arose in 1909; legislation came in 1946 and construction began in 1950. Burrendong Dam was completed in April 1965 and officially opened on 18 August 1967 by Robert Askin, the Premier of New South Wales. Its rock-fill wall is 76 m high and 1,116 m long, and the reservoir, Lake Burrendong, holds about 1,188,000 megalitres, with a further 480,000 megalitres of flood-mitigation space. It is the only dam on the main stem of the river; Windamere Dam on the Cudgegong is operated with it.
The dam does what it was designed to do. It has held floods that might have reached the plains, safely reaching 160% of capacity in 1990 and 152.8% in 2010, and the regulated river below it supplies irrigation schemes at Narromine–Trangie, Buddah Lakes, Tenandra, Trangie–Nevertire, Nevertire and Marthaguy. The Macquarie is classed as an over-subscribed river. In droughts the lake has three times fallen to about 1.5% of capacity, and it was reported at 1.6% in January 2020.
For the marshes the result has been fewer and smaller floods. Since the mid-1950s peak of 4,780 km², flooding has become both less frequent and less extensive, and the nature reserve, about 10% of the floodplain, is the area that still floods most reliably. The rest of the marshes, including large river red gum stands and some of the biggest bird rookeries, lie on private grazing and cropping land. Large floods still happen, as in November and December 2010 and in August and September 2016, and the marshes matter most as a waterbird breeding site in the aftermath of such floods.
The marshes are one small and unusually sensitive part of the Darling’s catchment. For the larger picture of how the rivers of inland New South Wales share their water, read our guide to the Murray–Darling basin, follow the water downstream in the Darling River guide, or compare the reed beds here with other kinds of wetland in what a marsh is.