SAN FRANCISCO (CBS SF) — A group of Bay Area athletes who attempted to swim the roughly 30 miles from the Farallon Islands to the Golden Gate Bridge for charity Thursday were forced to call it quits with only eight miles left to go.

With the San Francisco skyline in view after 13 hours of swimming through frigid, shark-infested waters, the six-member team of Night Train Swimmers was forced to call it a day at about 8 p.m. due to an unexpected change in the tides, their lead swimmer said.

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“It was a little demoralizing because we knew exactly where we were,” swimmer Phil Cutti said.

They had reached the stretch of waterway in which the group frequently trains and knew that, under proper circumstances, they could have completed the swim in roughly two hours, he said.

This was the team’s third attempt to complete the relay-style swim. They were forced to call off their first attempt in June 2010, after about five and a half hours in the water, when one of the swimmers began to experience hypothermia, Cutti said.

They tried it again this past March, but “barely made it out of the gate,” Cuttie said. Bad weather conditions in the wake of the earthquake and tsunamis that devastated Japan kept the swimmers from getting far.

Thursday’s relay took place in what is known as the Red Triangle, an area off the coast of San Francisco known for its abundance of marine life — including great white sharks.

The swimmers kicked off their swim shortly after 6 a.m. in 48- to 50-degree water, clad only in goggles, swim caps, and swimsuits—wetsuits are strictly forbidden, according to the group’s website.

Water temperature gradually increased to nearly 54 degrees throughout the day, but for these endurance athletes who train in similar conditions, the water temperature was not a problem.

“It was very doable,” Cutti said. “Not the most comfortable or pain-free, but doable.”

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The Night Train Swimmers plan carefully for weather and tide patterns but met an unexpected challenge Thursday night.

During such a long relay, the swimmers were prepared to work their way through both ebb and flood tides, Cutti said.

As they approached the bridge, they struggled through an ebb tide, which they had been expecting, counting on a flood tide to follow.

But due to the recent snowfalls, dams have been releasing water to compensate for the snowmelt. This release of water effectively created an artificial ebb tide and the anticipated flood tide never appeared, according to Cutti.

Waiting for the next flood tide would have meant waiting another 12 hours. Since long-distance swimming rules entail one swimmer to be in the water for each hour continuously, this was not a viable option, Cutti said.

But Night Train Swimmers is not ready to call it quits. The team, which formed in 2008, is already planning for the next venture, possibly in mid-May, Cutti said.

One thing that keeps them going is their commitment to charity, he said. This swim alone has raised tens of thousands of dollars for organizations and charities that support military members, their families, and veterans.

Organizations they donate to include the Wounded Warrior Project, Semper Fi Fund, and the Navy Seal Foundation, although contributors can choose to donate to a charity of their choosing on the team’s website at http://www.nighttrainswimmers.org.

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