LYNCHBURG, Va. -

As she navigated the world's busiest shipping lane last week, Sarah Dunstan thought of a phrase from the movie "Finding Nemo."

"It goes through your head over and over," said Dunstan.  "Just keep swimming! Just keep swimming!"

She had the line written on the front of her swim suit, custom made for her grueling adventure.

The English Channel is 21 miles long.  It's taken past swimmers anywhere from seven to more than 24 hours to cross it.

Thanks to great weather and calm water, Dunstan was on track to finish in about 13 hours.

"I really had an unusually beautiful day to swim in the channel," said Dunstan.  "It was a thrilling experience."

An experience that wasn't as hard as she expected.  At least not at first.

"The first six or seven hours were really wonderful," Dunstan said.  "Just euphoric and thrilling.  Then I started to tire."

The waters of the channel are cold, even in the summer.  Winds picked up as she got closer to France.

Then there were thoughts of the swimmers who've done this before, but didn't make it home alive.  A woman Dunstan knew had died a few days earlier, on the very same journey.

"It brings you back to the reality that this is an endurance sport and this kind of tragedy can happen," said Dunstan.

Eight hours in, Dunstan's boat captain told her she was still five hours away.

Pain finally took over.  She had to leave the water.

"A little bit of disappointment is creeping in that I wasn't able to finish, but I know that at the time I did the swim that I was able to do that day," Dunstan said Monday.

Now that she's home in Lynchburg, she's leaving open the possibility of maybe one day attempting the swim again.

Even if that doesn't happen, she's already had the adventure of a lifetime.

"I don't have the title of 'channel swimmer,' but I owned that eight hours in the channel and I was just so thrilled to be able to be there," said Dunstan.