[5] With a total length in excess of 186 kilometres (116 mi),[4] the Tambo River is one of the longest rivers in the East Gippsland drainage basin,[6] extending from the steep forested southern slopes of the Victorian Alps through forest and farmland to the Gippsland Lakes.

[7] The Tambo River rises in the Bowen Mountains, below Mount Leinster in the Victorian Alps, part of the Great Dividing Range, about 20 kilometres (12 mi) east of Benambra.

By the Swifts Creek and Ensay region the river is up to 12 metres (39 ft) wide, with deep pools of up to 140 centimetres (55 in), and a substrate of rubble and gravel.

In the steep forest sections between Ensay and Bruthen the channel width is up to 20 metres (66 ft), with a varying substrate of bedrock, boulders, rubble, sand and mud.

Between Bruthen and Tambo Upper there is extensive sedimentation with channel width exceeding 25 metres (82 ft), but a summer depth typically less than 50 centimetres (20 in).

[7] The riparian vegetation in the Swifts Creek/Ensay region is largely grass and willows, with little erosion of the banks or sedimentation present.

[7] The health of river has been impacted to various extents in its different sections by sediment run-off, and introduced weeds such as willows, blackberry and blue periwinkle.

Algal blooms related to sediment run-off have been seen in the lower Tambo system and the Gippsland Lakes.

According to Alfred Howitt the border between these two nations was around Tongio, about 10 kilometres (6.2 mi) north of present-day Swifts Creek.

[13] The name tambo is of uncertain origin, but is thought to be an Aboriginal Ngarigo word meaning "fish".

[13] The early explorers of Australia noted that the routes along the river and valley were well used Aboriginal trails, although in places such as the section between Tambo Crossing and Bruthen, where the river is less accessible, the trails diverted through the mountains in a similar way to the current main road through this area.

Another reason could be high water temperatures during summer, as small numbers of trout in the main river section have been found in cooler months.