Swimming across the English Channel — the 21-mile-long body of water separating southern England from northern France — is no easy feat. In addition to the strong ocean currents, swimmers also have to endure temperatures that can range from a chilly 64 degrees Fahrenheit (18 degrees Celsius) to a near-freezing 42 degrees Fahrenheit (6 degrees Celsius). However, don't tell that to Sarah Thomas. The 37-year-old American recently became the first person ever to swim across the length of the treacherous stretch of water, which links the southern part of the North Sea to the Atlantic Ocean, not once, but four times non-stop!