Australian marathon swimmer Chloe McCardel has successfully completed a world record 126km swim in the Bahamas.

McCardel’s support team says the 42 hour effort between two islands is the longest open-water solo, continuous marathon swim in history.

McCardel’s team say her effort surpasses a similar record set by Australian-British swimmer Penny Palfrey in 2011.

However, such claims come with complications.

The Marathon Swimmers Federation says it is difficult to compare marathon swims because currents vary in different locations and some previous efforts were not well-documented.

The 29-year-old athlete from Melbourne set out from the southern tip of Eleuthera island and reached the capital of Nassau at about 1am local time on Wednesday.

McCardel has previously swum the English Channel seven times, and last year was pulled from the water 11 hours into a swim from Cuba to the US after suffering venomous jellyfish stings to her throat and body.

McCardel has previously set records for swimming 60 laps across Bondi Beach and completing two non-stop double crossings of the English Channel.

She made this attempt under rules that included not being permitted to intentionally touch her support boat or hold on to anything.

Unlike the cold water swimming that McCardel experienced during her Channel crossings, the warmer waters of Caribbean diminished the risk of hypothermia; instead she dealt with heat stress, dehydration, stinging jelly fish and sunburn.

Her previous attempt to swim from Cuba to the US in 2013 almost ended in tragedy, after being stung by poisonous jelly fish 11 hours into the swim.

Suffering from multiple stings to her body and throat, she  ended that attempt prematurely.