| Castle Semple Loch | |
|---|---|
 Watersports on Castle Semple Loch | |
  Castle Semple Loch | |
| Location | Renfrewshire, Scotland |
| Coordinates | 55°47′N 4°36′W / 55.783°N 4.600°W |
| Primary inflows | River Calder |
| Primary outflows | Black Cart Water |
| Basin countries | Scotland |
| Max. length | 2.5 km (1.6 mi) |
| Max. width | 0.6 km (0.37 mi) |
| Settlements | Lochwinnoch |
Castle Semple Loch is a 1.5-mile-long (2.5 km) inland freshwater loch at Lochwinnoch in Renfrewshire, Scotland. Originally part of an estate of the same name, it is now administered by Clyde Muirshiel Regional Park as a watersports centre. An RSPB bird sanctuary is located on the loch's southern shore.