The River Quaggy (often the Quaggy River or simply Quaggy) is a river, 17 kilometres (11 mi) in length, passing through the south-east London boroughs of Bromley, Greenwich and Lewisham. In its lower reaches it is an urban river, in its upper reaches further from London it is more natural and known as the Kyd Brook. The river rises from two sources near Princess Royal University Hospital (PRUH) at Locksbottom and is a tributary of the River Ravensbourne which it flows into near Lewisham station in Lewisham.

A long stretch of Kyd Brook is visible in Hawkwood, an area of open farmland and countryside upstream of Chislehurst that is owned and managed by the National Trust, but open to the public free of charge. From there the river flows northwards through Sundridge Park Golf Course then on across Chinbrook Meadows between Chinbrook and Grove Park, then through the outer parts of Mottingham, Middle Park, Horn Park, and Eltham. The river then enters Sutcliffe Park and starts to flow west through southern Kidbrooke, and Blackheath then finally through Lee and its park Manor House Gardens into Hither Green then Lewisham where it joins the River Ravensbourne next to Lewisham station. In Sutcliffe Park, the river used to run under the road and via a covered culvert through the park. This was remodelled several years ago to reintroduce a flood area to protect areas further down stream. Also this created a marshy area for wildlife to return. It is now an oasis full of wildlife in the middle of two major roads.

As part of the Ravensbourne catchment area, the river is kept constantly under inspection by the Environment Agency which issues flood warnings when applicable.