People taking selfies next to crocodiles at a Top End nature park have been warned - you are at risk of being attacked.

The reputation of the large, aggressive saltwater crocodile is constantly on display to people visiting Top End nature reserves and the coastline, with signage and other information in several languages warning of the deadly power and ambush tactics of the animals, which can grow to over five metres.

However the smaller, meeker freshwater crocodile, locally referred to as "freshies", can often go without a mention.

But the Parks and Wildlife Commission of the NT (PWCNT) have issued a warning after what it said was "recent reports of risky behaviour" of people getting too close to freshies for photo opportunities at Fogg Dam Conservation Reserve, about 70 kilometres east of Darwin.

"The freshies have even been seen sunning themselves up on the dam wall, which has given visitors a great opportunity to see these fascinating crocodiles in the wild," PWCNT's Michael Barritt said.

"Sadly, there have been some visitors that have taken the opportunity for a snappy selfie with these wild animals and have been striking a pose with them by getting incredibly close."

Authorities are warning people of the dangers of taking photos near crocodiles at Fogg Dam, in Darwin's rural area. ( YouTube )

Saltwater crocodiles, locally known as "salties", have the strongest jaw power of any animal, with scientists in 2012 recording a croc's bite force of 3,700psi (pounds per square inch) or 16,460 newtons.

This is about equal to the weight of a crew cab truck. By comparison a human's bite force is about equal to the weight of a sack of potatoes.

Signage along waterways and tourism brochures in the Northern Territory often feature the cartoon silhouette of the saltwater croc, jaws open, to warn of the peril.

The smaller stature, narrower jaw line and more timid nature of the freshwater crocodile species features much less in official communications.

Mr Barritt said although freshies were considered less dangerous than their saltwater relatives, that did not mean an attack would not happen.

"Freshies can give a nasty bite with their razor shape teeth if they feel threatened and approaching too close is enough to make them feel threatened.

"The smallest wound will usually get continually infected as well," Mr Barritt said.

He advised people "keep a safe distance of at least 15 metres" from freshies.

He said waters levels at Fogg Dam meant visitors would be rewarded with a variety of waterbirds and other wildlife, but along with those sights came the ever present danger of crocs, of both kinds.

"A massive 4.25-metre saltie was caught just under two years ago," Mr Barritt said.

"Public safety is our top priority which is why we have a permanent trap set at Fogg Dam."

Seven saltwater crocodiles have been removed from Fogg Dam since 2013 and walking on the dam wall is prohibited due to the risk.

Mr Barritt urged people to remember that "croc danger is real".

"Don't risk your life," he said.