The River Greta is a river in Cumbria, England. It is a tributary of the River Derwent and flows through the town of Keswick.
The source of the river is to be found near to Threlkeld at the confluence of the River Glenderamackin and St. John's Beck. From thence, the river runs westward, roughly aligned with the former Cockermouth, Keswick and Penrith Railway between Keswick and Penrith, the course of which is now walkable.
The river subsequently flows through Keswick before joining with the Derwent just after the latter flows out of Derwentwater.
The major tributaries of the Greta are Naddle Beck and Glenderaterra Beck.
River Greta in Fitz Park Keswick, with Penrith Road on the right
River Great in Fitz Park Keswick, looking towards the town