A stench that has permeated over some Darwin suburbs in recent days has sparked an investigation by the Northern Territory's environmental watchdog, with conflicting reasons as to what is causing the offensive odour.

Foul "rotten-egg" type smells have been noted over some northern suburbs, including Leanyer, Muirhead, Lyons, Malak and Anula, with a sewage plant at Leanyer the likely culprit.

After more than 30 complaints in the past 10 days, the NT's Environment Protection Authority (EPA) has launched an investigation.

"We have initiated a formal investigation and I can't say too much about that, but you can rest assured that we are on top of it and we have already taken some initial action as well," EPA director of environmental operations Peter Vassal said.

"My officers were up to 11 o'clock last night investigating odours, and that is one of a number of nights they have been out there, and days, and they have detected what you describe as offensive off-site odours."

Hot weather blamed

Water services general manager John Pudney from the Power and Water Corporation admitted there was an "issue" and blamed hot weather.

In recent days Darwin and other parts of the Top End have been hit by higher-than-average temperatures.

"We have looked at our in-stream and in-pond temperature gauges," Mr Pudney said.

"It is actually a significant weather event that has happened over the last week or so.

"That has exacerbated the ponds."

Mr Pudney said the weather had caused a "temperature inversion" where the bottom layer of the ponds had mixed with the top layer, bringing with it foul smells.

"This happens occasionally, and it exacerbates the situation and also we have had the still air in the morning and in the evening, so you sort of get odours trapped in the valley, if you like," Mr Pudney said.

EPA has a different view

However, Mr Vassal did not agree with that explanation.

"We have a variance on the cause of the issue and that is what we are following up with Power and Water," he told ABC Radio Darwin.

"I can't say too much but we are obviously of a different view.

"We believe there were actions that could have been taken to ameliorate the situation but that is part of the investigation."

He also rejected claims from Power and Water that the smells would have been unlikely to have reached Anula, a suburb about four kilometres from the sewage ponds.

"My experience has been from Waste water treatment plants they [odours] can go many, many kilometres offsite, so I don't agree with that," Mr Vassal said.

Meanwhile, Darwin's new Lord Mayor Kon Vatskalis, who was sworn in this week, said he found the situation unacceptable and had lodged a complaint.

"I understand we have to have the waste water treatment plant - other cities do have them - but other cities do not have the same problem," Mr Vatskalis said.