SAN FRANCISCO—A great white shark prevented marathon swimmer Simon Dominguez from becoming the first to swim from the Golden Gate Bridge to the Farallon Islands.

Dominguez, 49, set out into the 50-degree water with a cap, goggles, and his swimsuit. His only defense against the elements was a thick coat of grease intended to ward off jellyfish stings.

“I’ve trained for much colder water than it’s going to be out there,” he told CBS San Francisco. “I just want to get in the water and get this swim done.”

His 16-year-old daughter, Olivia, followed his progress in a support boat stocked with protein drinks and other supplies.

He was just three and a half miles away from the rocky shore when Olivia spotted a great white shark circling her father. The shark was estimated to be 12 to 15 feet long, and was possibly attracted by the blood from Dominguez’s chaffed skin.

After 18 hours in the water, Dominguez reluctantly climbed into the support boat.

“It was hard,” he said to CBS San Francisco. “But a shark is a shark.”

Dominguez said that he would have to check with his wife and daughter before attempting the swim again.

Four swimmers have made the 30-mile journey from the Farallones to the California coast, but Dominguez was the first to attempt the solo swim in the other direction.

Dominguez trains with open water swimming group Night Train Swimmers. The group was founded in 2008 by a team training to complete a relay crossing of the English Channel. Night Train Swimmers have since made it their goal to complete at least one large swim per year.

Fellow Night Train swimmer Kimberly Chambers will also be attempting to make the record Golden Gate Bridge-to-Farallones swim sometime in August.