NT Parks and Wildlife rangers Chris Heydon and John Burke said it is very unusual to capture a croc this big in the Katherine River system.

“We average a 4.2 metre croc most years, but never this big,” ranger Burke said.

Rangers observed three large crocodiles during aerial surveys in May.

Traps went in two weeks ago and the biggest was the first to be hit, ranger Burke said.

“Capturing more crocs downstream makes it less likely we’ll find any closer to the Katherine town,” he said.

Rangers said the 600 kilogram croc, who might be over 60 years old, was not as difficult to trap as one would think.

“When they are this big we just sedate them, so there is no chance of us getting chomped,” ranger Heydon said.

The unusual dry season capture reinforces the warnings of Parks and Wildlife to avoid swimming in rivers and streams in the Northern Territory.

“Although this is the biggest we’ve caught in the Katherine River, there are bigger ones out there that come up from the Daly River,” ranger Burke said.

“Even though it is dry season, crocs are around. They are always moving around regardless of the temperature,” he said.

“The population is growing. Stay vigilant.”

There have been a number of captures in the Katherine River already this year.

Two large salties, 3.92 metres and 3.97 metres, were taken from a trap just downstream of the high level Katherine bridge in February and March this year.

Five metre salties are considered a rarity in NT’s inland waters.

A 6.4m saltwater crocodile was caught in a net on the Mary River in 1974. The animal was killed and its head removed by an axe.

The biggest saltwater crocodile ever caught in a trap was just over 5 metres long.

According to the NT Government, there have been 188 saltwater crocodiles captured in the Top End this year.

There have been seven pulled from the Katherine River already this year, against 13 last year and eight the year before.

It has led to calls to cull crocodiles because of public safety and fear they are driving tourists away.