The swimmers have decided to end their swim in Whitby on Saturday after one of the swimmers was overcome by hypothermia on Friday afternoon.
A tweet from Durham Search and Rescue said "18-year-old Lake Ontario swimmer Mona Shariri pulled from water in Newcastle due to hypothermia."
Shariri is the youngest member of the team which was aiming to raise money for the Because I Am A Girl campaign.
A post on the group's Facebook page said, "After 4 gruelling days of swimming in ever changing conditions we've decided to change our landing destination to Whitby. We've had an extremely challenging swim, but are glad we've made it as far as we have."
A spokesman for the team said in an email to CBC News, "It's ending at Whitby at 2:00 p.m. [Saturday] Heyden Shore Park in Whitby. Bottom of Brock St. I will have an alert out at 8:30 a.m. It's is ending for sure."
The group set out on Tuesday hoping to be the first group to swim the lake from east to west in a gruelling 305 kilometre relay they expected to result in five straight days of non-stop swimming.
The women - who range in age from 18 to 61 - swam in two-hour shifts through the day and night, sleeping and eating on an entourage of sailboats and zodiacs.
All of the women are accomplished long-distance solo swimmers. Colleen Shields, 61, Nicole Mallette, 48, Samantha Whiteside, 23 and Rebekah Boscariol, 18, have successfully completed the Lake Ontario crossing.
Sharari swam across the English Channel last year.
The length-wise crossing has never been completed, but the solo crossing from Niagara-on-the-Lake to Toronto has been completed 57 times, the majority of them by women.
The crossing was first completed by Marilyn Bell in 1954, when she was 16-years-old.
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