Margaretha Pedder (born 27 June 1980) is an English former competitive swimmer who specialised in butterfly events.

During her sporting career, Pedder trained with the Portsmouth Northsea Swim Club under head coach Chris Nesbit and later at the University of Southern California under Mark Schubert.

Swimming in heat four, she escaped from last at the turn to edge out Finland's Marja Pärssinen by 0.41 seconds for the seventh seed in 1:01.53.

[5][6] Three days later, in the 200 m butterfly, Pedder advanced to the top 16, and finished her semifinal run with an eleventh-place time and a lifetime best of 2:10.49.

[11][12][13][14] Pedder also competed in U.S collegiate swimming for the University of Southern California, where she became a three-time All-American in the mile and 800 freestyle relay.