It took just under 10 hours for ocean swimmer Louise Stevenson to finish her marathon swim for Christchurch.

The champion swimmer, 30, completed a double crossing from mainland Fiji to Beachcomber Island and back in nine hours and 45 minutes. She raised $20,150 for her quake-hit home town.

Stevenson told The Fiji Times Online she was motivated by health, fitness and "doing something no one else has done yet".

Stevenson swam from the Sofitel Resort and Spa Beach to idyllic Beachcomber Island and back through the Mamanuca Islands.

The Fiji Times reports that Stevenson was supported on a nearby paddle board by fellow surf lifesaver and Australian champion board paddler, Becci Gardener, and received nutrition in the form of gels during the course of the swim.