McCardel's past swims include twenty-nine solo crossings of the English Channel, including eight crossings in one season and three crossings in one week, three double-crossings in 2010, 2012 and 2017 and, in 2015, the fourth person to do a non-stop triple-crossing. She also won the 28.5-mile Manhattan Island Marathon Swim in 2010. As of Summer 2015, she holds the world record for the longest ever unassisted open-water swim, at 128 km.
Australian Record
On 22 October 2016 McCardel completed her 20th solo swim across the English Channel. She set a new Australian crossing record, taking the previous record from Des Renford.
On 22 October 2014 McCardel completed an unprecedented swim from South Eleuthera Island to Nassau, Bahamas. 124.4 kilometers in 41 hours, 21 minutes. She set a new world record, longest unassisted ocean swim, conducted under the ‘Rules of Marathon Swimming’. This swim was officially ratified by the Marathon Swimming Federation. The Rules of Marathon Swimming are a globally-endorsed framework of rules and guidelines for any swim in any body of water. The Documented Swims program offers a venue for publishing documentation and requesting peer-reviewed ratification of independent marathon swims. She also won the 2014 MSF ‘Solo Swim of the Year’ for this World Record swim.
Record attempt
On 12 June 2013, she attempted to be the first person to swim across the Straits of Florida from Cuba to Florida without using the protection of a shark cage. She also did not wear a stinger suit or a wet suit. This swim was done to raise funds for three charities; the CanTeen, Can Assist and Swim Across America. McCardel had a 32-person support team that included weather experts and doctors that accompanied her throughout her trip, which was to last about 55–65 hours. She was to eat and drink every half hour. After 11 hours, McCardel stopped her record swim attempt after she was severely stung by multiple box jellyfish and was in too much pain to continue. She was taken to Key West and was treated for the stings.
Coaching
Across June/July 2015, McCardel, with the support of her team, coached seven relay teams and three solo swimmers to swim the English Channel. Two of these relays were from the Geelong Grammar School. Geelong were part of the "Channel Conquerors" program which also featured two school age Relay teams from The Arch Academy – coached by Dan Simonelli. In 2014, she coached and crewed 2x relays to swim the English Channel. These swimmers raised over US$125 000 for a cancer charity – Swim Across America. In July 2015, she also coached and crewed one of the 2014 English Channel relay fundraisers, Grant Wentworth, to swim between Cape Cod and Nantucket and, in doing so, raising $150 000 for Swim Across America.
