Grandma, 55, becomes first swimmer ever to complete grueling 29.7 mile swim from San Francisco to Farallon Islands after 17 hour marathon through freezing waters filled with great white sharks

A grandma has become the first swimmer to ever complete a grueling 29.7 mile swim from San Francisco to the Farallon Islands.

Amy Appelhans Gubser, 55, completed the herculean effort on May 11 after 17 hours in freezing, great white shark-infested waters. 

The pediatric nurse was the first to cross the treacherous Gulf of the Farallones swim in the outbound direction and only the sixth to do it either way.

The outbound route is much harder as it is against the wind and choppy currents.

'It was the toughest thing that I have ever set out to do,' Gubser told the San Francisco Chronicle.

A grandma has become the first swimmer to ever complete a grueling 29.7 mile swim from San Francisco to the Farallon Islands

Amy Appelhans Gubser, 55, completed the herculean effort on May 11 after 17 hours in freezing, great white shark-infested waters.

The pediatric nurse was the first to cross the treacherous Gulf of the Farallones swim in the outbound direction and only the sixth to do it either way

The outbound route is much harder as it is against the wind and choppy currents

Like all open water marathon swimmers, Gubser was not allowed to wear a wetsuit when she plunged into the icy waters at around 3.30am.

'I was pretty steady for the most part, but at the end we hit a strong current and the water got colder,' said Gubser. 

'My progress was slowed because I was chilled to the bone. I did not expect 43 degrees. That was nuts.' 

Gubser was assisted by a support team made up of pilot Chad Dahlberg of Pacific Rival Fisheries, and SERC swimmer John Chapman, Abby Fairman, Kirk McKinney, Ken Mignosa, Sarah Roberts and John Sims. 

Roberts, McKinney and Mignosa each swam some of the route with her. However, rules only allow for an hour of support swimming at a time, with an hour in between.

When she felt like throwing in the towel, Gubser said her thoughts turned to her stepbrother, Dan Fine, 67, who is dealing with stage four pancreatic cancer. 

'I wanted my kids to be proud of me, and I wanted my grandkids to be proud of me,' said Gubser. 

'I want to support other swimmers this summer to help them achieve their goals. I just hope I can inspire others to challenge themselves.'

Like all open water marathon swimmers, Gubser was not allowed to wear a wetsuit when she plunged into the icy waters at around 3.30am

She was assisted by a support team including swimmers who were only allowed to accompany her for an hour at a time each with an hour break between

Gubser is a married mom-of-two and grandma of two, with a third on the way

To prepare for her record-breaking swim, Gubser rose before dawn up to three times a week to train for hours before work at 7.45am

 Gubser is a married mom-of-two and grandma of two, with a third grandchild on the way. 

She has been swimming her whole life and grew up swimming around Manhattan and Hermosa Beaches in Los Angeles.

To prepare for her record-breaking swim, Gubser rose before dawn up to three times a week to train for hours before work at 7.45am.

'I believe the swim between the Farallon Islands and the mainland is the toughest marathon swim in the world,' said Evan Morrison of Sydney, co-founder of the Marathon Swimmers Federation. 

'Amy's endurance in cold water is unparalleled. There are no more than two or three people who could even have a chance at doing what she did. Her ability is world class.'  

After completing the mammoth journey, Gubser posted on Facebook: 'I had a little swim this Saturday!

'This was NOT possible without my well prepared and seasoned crew!! 

'Had some major logistical changes just a few days before this swim and could NOT let this derail our swim - I say OUR swim because it wasn’t possible without each member of this team!'