The Molonglo catchment comprises approximately 212,000 ha within the Murrumbidgee catchment in south‑eastern NSW and the ACT. It includes all the land that drains into the Molonglo River and Lake Burley Griffin, including the Queanbeyan River, and all the tributaries.

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The catchment encompasses parts of the Queanbeyan‑Palerang Regional Council and Snowy-Monaro Regional Council, and part of the ACT. Included within the boundary is the entire city of Queanbeyan and a portion of the central suburbs of Canberra.