A California man’s goal to swim almost 30 miles between the Golden Gate Bridge and the Farallon Islands was thwarted on Thursday when a great white shark was spotted near his finishing mark.

Corte Madera marathon swimmer Simon Dominguez's teenage daughter, in a support boat, spotted the shark about 3 ½ miles from the Farallon Islands, KPIX-TV reported.

After 18 hours in the frigid ocean, Dominguez reluctantly climbed into the boat as the 12-to-15 foot shark circled it. The 49-year-old, with blood streaming down his chest from chafed skin around his neck, said he was disappointed he couldn’t finish the swim.

"It was hard. But a shark is a shark," Dominguez said.

Four swimmers have swum from the Farallon Islands to San Francisco, but Dominguez was determined to be the first to make the trip in the other direction.

The islands are a breeding ground for great whites, but Dominguez said he decided to make the attempt in the summer before the typical start of the breeding season in the fall.

The 240-pound swimmer jumped into the cold ocean and began the swim under the Golden Gate Bridge Tuesday night, wearing only a cap, goggles, swimsuit and a thick coat of grease to guard against jelly fish stings and keep him a little warmer in the 50-degree water.

After giving up the swim, he said his only plans at the moment were to "go straight to the pub, have a few beers and decide what the next steps are."

The Associated Press contributed to this report.