Katie Ledecky managed to secure her fourth gold of the Rio Olympic games in the pool on Friday night in a sensational win in the Women's 800m freestyle final.

The 19-year-old's performance was spectacular as she appeared almost half a pool length ahead of her fellow competitors, as she reached the final 50 meters.

With just 300 meters of the race left to go, Ledecky was far, far ahead of her own world record, and well ahead of the other swimmers who were left trailing in her wake. 

For the final minute-and-a-half of the race, Ledecky was so far ahead that television cameras were unable to even feature the other swimmers in the same frame. 

By the time she completed the race, Ledecky was a full 12 seconds ahead of everyone else in the field.

The Washington DC native won her fourth gold of these Olympics and fifth in all.

She has become only the second woman to sweep the 200, 400 and 800-meter freestyles.

'I think i did a pretty good job. I think I'll be happy with it! Swimming in front of a crowd like this, I am so happy', she told NBC after getting out of the pool. 

Jazz Carlin of Britain won silver, while Boglarka Kapas of Hungary claimed bronze. 

Ledecky led from the start to clock eight minutes, 4.79 seconds, beating her previous mark of 8:06.68 set in Austin, Texas in January.

Britain's Jazz Carlin took her second silver medal in 8:16.17, and Boglarka Kapas of Hungary took the bronze.

Ledecky, defending Olympic champion at the distance, added to her golds earlier in the week in the 200 and 400 freestyle and the 4x200 freestyle relay, plus a silver in the 4x100 relay.

The only previous woman to win the 200, 400 and 800 freestyle at the same Games was American Debbie Meyer in 1968. 

Ledecky sliced 1.89 seconds off her own record in what is the longest event of the women's swimming programme.

It was the seventh world swimming record of the Rio Games, and the second by Ledecky, who achieved a similar feat in winning the 400 freestyle.

Since winning the 800 in London four years ago, she has been invincible, and anything but a victory would have been one of the biggest shocks of the Games.

Carlin and Kapas fought a dogged struggle for second, with Spain's Mireia Belmonte Garcia challenging them for much of the way.

Meanwhile, Anthony Ervin of the United States reclaimed the mantle of fastest man in the water on Friday by taking the Olympic 50 meters freestyle gold medal 16 years after he first won it, and by the slimmest of margins.

France's Florent Manaudou, the defending champion, finished second and just 0.01 seconds behind the 35-year-old veteran, who won in 21.40 seconds.

Nathan Adrian of the United States took the bronze.

Ervin won his first individual gold medal in a dead-heat in the same event with team mate Gary Hall Jr at the 2000 Sydney Games. Both touched out in 21.98 seconds.

Sixteen years after winning his first individual gold medal at the Olympics, Anthony Ervin picked up his second with a furious dash from one end of the pool to the other.

Completing a remarkable journey in the blink of an eye, the oldest member of the U.S. swimming team touched first in the 50-meter freestyle, edging the defending Olympic champion, Florent Manaudou of France, by a mere hundredth of a second. 

The 35-year-old Ervin won his first gold at the 2000 Sydney Olympics, tying teammate Gary Hall Jr. for the top spot. Then, Ervin walked away from swimming, skipping the next two Olympics while he embarked on a journey to find his purpose in life.

Turns out, it was swimming all along. He returned to make the American team in 2012, but failed to win a medal in London. 

Now, improbably, he’s back on the top of the podium again.

Simone Manuel, who became the first African-American woman to win an individual Olympic swimming event on Thursday night also managed to qualify for the women's 50m freestyle event which takes place on Saturday.

The women's 50m freestyle semis were delayed for more than half an hour on Friday night after reports that a bus carrying the participants got lost.