A Darwin couple has revealed an ordeal that saw them wade through crocodile-inhabited waters to be airlifted to hospital, when the woman fell unconscious after being bitten by a March fly.

Husband and wife, Allan and Zerena Di-Prima, told ABC Tales from the Tinny how a typical day of fishing in Leaders Creek, about six weeks ago, took a dramatic turn after they became marooned by a low tide.

Once the couple made it to safety, doctors told them Ms Di-Prima had suffered a severe anaphylactic reaction.

"March flies can be pretty vicious up here," Ms Di-Prima said.

"I had a bad bite on my toe and it was really hurting, like more than usual.

Sorry, this audio has expired Woman paralysed by March fly. Carried out of croc country by hero husband

"My whole body started to come up with hives and a rash. I started freaking out a little bit, my sight started to go in and out.

"Allan was yelling at me like, 'How many fingers have I got up' and I just couldn't see anything, it just faded to black and I passed out."

Ms Di-Prima's husband Allan then tried to bring her back into consciousness by pouring cold water over her, all the while trying to return to the boat ramp.

"Then she started convulsing and her eyes rolled back in her head, she started flopping into the front seat," Mr Di-Prima said.

"She had absolutely no motor functions at all ... I just kept trying to get to the ramp because it was the only way I knew to get her to safety.

"Unfortunately with the low tide, I knew there was no way we could even make it back to the boat ramp."

'I was nearly dry-retching because of thirst'

Mr Di-Prima got out of the boat to push it through waters inhabited by crocodiles, with the boat ramp still about 700 metres away.

"I was just in survival mode just trying to get back and get some help," he said.

Once the couple waded to land, a Careflight helicopter airlifted Ms Di-Prima to hospital. ( Facebook: Careflight )

"Out of nowhere she came to, and started talking to me, we both hopped out of the boat and I said, 'We've got to go, we've got to walk to the ramp'.

"The mud was well over my knees and depth and I was trying to carry her through it and trying to get her to help me get over some rocks, a few wood holes where there could've be a good sized croc or something like that hanging out," Mr Di-Prima laughed.

"And because I poured all the cold water over Zerena, I ran out of water myself, so I was nearly dry-retching because of thirst."

After wading through the muddy mangrove waters for 700 metres, Mr Di-Prima raised the alarm.

A Careflight helicopter soon arrived and airlifted the couple to Royal Darwin Hospital with Ms Di-Prima still drifting in and out of consciousness.

March fly bite caused anaphylactic reaction

Ms Di-Prima said doctors were certain it was caused by a severe anaphylactic reaction to the single March fly bite on her toe, but she had never been allergic to anything prior to the incident.

Zerena Di-Prima and her husband Allan were fishing in Leaders Creek. ( Supplied: Zerena Di-Prima )

"Before that [the anaphylactic reaction] I had started getting big welts coming up every time I was bitten, and they [doctors] just think it built up and my system was like, 'Nup'," Ms Di-Prima said.

"So it could pretty much happen to anyone."

The couple said they were not deterred from future fishing trips, but will be more prepared for the unusual.

"If you know you have anaphylactic reaction to things, make sure you take that Epipen with you, plenty of water, all your safety gear," Ms Di-Prima said.

"And always take a fishing buddy, because one day it could save your life."

'Tryphera' species may be to blame: Entomologist

A species of March fly that causes anaphylaxis is called the "tryphera" and is less than a centimetre long, Darwin medical entomologist Peter Whelan said.

"It's relatively common to be bitten by this species but it's quite uncommon to have anaphylactic shock, [however] there is an elevated risk of anaphylactic shock with that species, as opposed to regular March flies," Mr Whelan said.

"This one in particular, and a lot of March flies in general, are attracted to dark round shapes, and particularly blues."

The best way to avoid being bitten is to wear white or light colours, use insect repellent and swat away the slow-flying insects, Mr Whelan said.

The flies are widespread through the NT and the Top End, Mr Whelan explained, and prefer wetland areas, waterways with mixed fresh and saltwater, and anywhere with rotting vegetation.

He said the bite was painful because the biting apparatus was not fine like a mosquito, but more like a "jack-hammer".

"They jackhammer a bit of a hole, and then they push saliva down into that hole and then suck the blood out, but the saliva has anti-clotting chemicals in it and included in that will be some foreign proteins," Mr Whelan said.

"And the foreign proteins are the sort of things that ... set up a reaction, so for a relatively small number of people that could lead to a severe reaction which could lead to anaphylactic shock."