Lake Monger (Noongar: Galup,[3] Keiermulu[1]) is a large urban wetland on the Swan Coastal Plain in suburban Perth, Western Australia nestled between the suburbs of Leederville, Wembley and Glendalough.

[5][6] The lake was originally part of a series of freshwater wetlands running north from the Swan River along the coastal plain for approximately 50 kilometres (31 mi).

The myth describes the track of a serpent being, who in his journey towards the sea, deviates from his route and emerges from the ground which gives rise to Lake Monger.

[2] In 1829, a British expedition established the Swan River Colony and in 1830, Lake Monger was the site of minor skirmishes between white settlers and Noongar men, one of which was Midgegooroo.

[10] A site was allocated in 1833 as a "reserve" and food depot for Noongar people, a decision of the government that was sharply rebuked by Robert Menli Lyon.

[12] In 1909, construction of a drain was completed which connected the lake with the Swan River and which allowed the water level to be managed.

[12] From the early 1920s, the newly formed City of Perth started acquiring land which was until then being used as Chinese market gardens and dairies for conversion into public parks and recreation areas.

[13] After many years of delays due to lack of funds, silt dredging works commenced in May 1932 to reclaim 20 hectares (49 acres) of the mainly swampland.

A "swim-through" on the lake was held as part of the celebrations, as well as a canoe race involving Leederville, Wembley and Mount Hawthorn Boy Scouts and a series of bonfires.

[7][12][14] As well as dredging silt, reclamation was assisted by the dumping of rubbish and raw sewage from night soil collectors on the north-eastern side.

In 2019, a strong smell that permeated the north east part of the lake for several years was found to be caused by rotting algae.

None of the banksia and few paperbarks remain and trees are now generally confined to a narrow strip surrounding the shoreline, mainly on the northern and eastern sides.