Wendy Bank, a 47-year-old mother of three from Boulder, wanted something unique to give her husband for his 50th birthday. Bank went big: She formed a team that would attempt to swim across the English Channel.

The Denver Post writes that Bank’s husband, Holden, was initially skeptical, but he embraced the plan when the couple decided they’d use the adventure as a way to raise money for the Special Olympics and the Leukemia & Lymphoma Society.

Still, saying you’re going to swim, relay-fashion, across the narrowest span of the English Channel—21 miles—is the easy part. The Banks and the four friends Wendy Bank (pictured) recruited have been training since April, swimming up to an hour at a time in the cold water of lakes and reservoirs around northern Colorado.

Even in the friendly confines of their home state, the swimmers face the distinct risk of hypothermia, a threat that is often mixed with jellyfish and sharks, as well as seven-foot swells and powerful currents, once the swimmers enter the unforgiving waters of the English Channel.

The crew will have a support team and a qualified captain calling the shots, requirements established by area officials. Those European officials will also determine when the swimmers can begin their trek, which might start any time between Thursday and June 30.

Whatever happens, the swimmers and their supporters will chronicle the adventures via their blog, Mile High Chunnel Toppers.