It is nearly 4m long, weighs at least 317kg, and yes, it is a real alligator.

Social media users were stunned when a photo of a massive alligator in an irrigation ditch in the United States hit the headlines last week.

A farmer had alerted officials from the Georgia Department of Natural Resources to the giant reptile on the west side of Lake Blackshear on Feb 25.

According to local media reports, the alligator had been in the ditch for about a week before it was rescued.

Wildlife biologist Brent Howze told Canadian broadcaster CBS News that the alligator had several injuries, including what appeared to be old gunshot wounds.

Upon assessing its condition, the wildlife team decided to put it down due to its poor health and old age.

Mr Howze, however, was captured in a photograph kneeling next to the alligator before it was euthanised.

The photo quickly went viral, with social media users in disbelief that such a large alligator actually exists. Many of them also questioned if the photo was a hoax.

However, local newspaper Cordele Dispatch sought to quell the rumours last Thursday (Feb 28).

"Apparently a lot of people think it's fake, but I can assure you that it is not," Mr Howze told the newspaper.

"I'm the one in the picture, and you can probably tell that I didn't get too close to it."

He said that the alligator had a chest girth of about 1.4m.

Alligators of this size are rare, though unsurprising, as male alligators are known to be able to reach up to 4.2m, he added.

Despite its intimidating size, Mr Howze said that the reptile poses almost no threat to humans.

Rather, they are able to reach such a size only when they stay away from people.

"There's only one way for an alligator to live this long, and it's by avoiding humans," Mr Howze said.

"I'll be in the water at Lake Blackshear this summer for sure."