Troyden Prinsloo braved tough conditions to finish in 12th place at the marathon swim on Friday.
His time was 1:50.52, with Oussama Mellouli of Tunisia winning in 1:49.55. The Tunisian made history by becoming the first person to win Olympic medals in both the pool and open water races at the same Games, having already won bronze in the 1 500.
"This is all new to me," said Prinsloo afterwards. "I swam my race but was not too sure how fast to go or when to push. I am happy with the position I got here today even though I would have liked it to finish in the top ten and I am not too sure what my time was."
This is only Prinsloo's third major international meet in the marathon swim, the first being the World Championships last year in Shanghai and the second his second qualifier in Portugal earlier this year.
The swimmer said he hoped to get some funding as he would like to continue in the open water and try and get to the Rio Olympics.
"I will speak to my coach Nick Gray first. He will help me analyse my race and then we will take a decision of what to do next," he said.
He said he expected Mellouli to win the race.
"He was unbelievable in Portugal and I expected the same here in London," said the former student from the University of Georgia in the US.
Prinsloo said he suffered on the fifth lap where he fell to the 17th position, but fought hard to swim back up to12th spot. He was also shown the yellow flag (a warning) on the first lap but said he was not too sure what he'd done wrong.
His time today was slower than his qualification time in Portugal of 1 hour 44 minutes.
"I have a lot to learn. With more experience I can probably try and medal at the 2016 Rio Olympics"
"I will not really take time off because if I have the means I would like to compete at two more events in the World Series, in September and October. So there will not be a lot of time to take off.
"It is something that I will do for a few years as most of the swimmers I compete against are about three to four years older than me and that was the difference today – they all have far more experience in the open water," he said.
"I have a lot to learn. With more experience I can probably try and medal at the 2016 Rio Olympics, but funding will always be the main problem," said Prinsloo.
"I am very lucky that Speedo and PeptoPro decided to sponsor me. It helps, but it is still a struggle out there as a professional swimmer. I am still looking for more sponsors," he said.