The River Winster is a river in the English county of Cumbria. The Winster was the boundary between the ancient counties of Lancashire and Westmorland. It has a relatively small catchment area; other streams flow parallel to it on either side.
The Winster is about 20 km or 12 miles long, and rises about 2 km south of Bowness-on-Windermere, between the hamlets of Winster and Storrs (the latter is on Windermere) and follows a southerly course, flowing past the settlements of Ludderburn, Hartbarrow and Bowland Bridge, before it is joined by Arndale Beck at Bridge House.
From there, the river continues through a valley between Whitbarrow and Cartmel Fell, flowing through Helton Tarn. It continues between the villages of Lindale and Meathop, and finally flows into the Kent estuary just downstream from Arnside.
A former course of the river joined the Kent at Blawith Point, and as a result the peninsula of Holme Island often changed hands between Lancashire and Westmorland.
There are two packhorse bridges on this river near Winster. The Winster Bridge (1729 with 20th-century parapet) on the river at  Another packhorse bridge (Probably 17th-century. Grade II listed) is on a tributary of the River Winster at , adjacent to A5074 road.
- Holme Island, BBC Cumbria. Retrieved 11 September 2006.
- "Packhorse Cargo". cottontown.org. Retrieved January 9, 2007.
- "Winster Bridge (That Part in Cartmel), Cartmel Fell". britishlistedbuildings.co.uk. Retrieved 13 November 2012.
- Grade II: buildings that are of special interest, warranting every effort to preserve them.
- "Pack Horse Bridge Beside A5074 a Quarter of a Mile North West of High Mill House, Crook". britishlistedbuildings.co.uk. Retrieved 19 November 2012.