A water aerobics class in Darwin had to be postponed this morning after a crocodile entered the pool.

The 1.5 metre freshwater croc was spotted in the Howard Springs Holiday Park pool about 30 minutes before the class was due to start.

"We went down like normal to check the pools out - chlorine and test them, give them a scoop out -because [on] Tuesdays and Thursdays the local ladies of Howard Springs do their water aerobics," the park's manager, Geoff Thompson said.

"And there was a crocodile in there."

He said none of the women were keen to start the class at the scheduled time.

"They were all there waiting for the ranger to collect it and once he got it out of the water they started their aerobics," he said.

Mr Thompson said he first thought someone must have deliberately put the croc in the pool because it has a fence around it.

But he now believes it slipped under a section of the fence.

Parks and Wildlife senior ranger Tom Nichols said his team removed the crocodile about 9am.

"The crocodile gave one of the crocodile management rangers a bit of a run around, having to chase it around the pool, but he managed to capture and remove it with a scoop net," he said.

"The crocodile did not have any markings so we believe it to be a wild animal.

"While we can't be sure how it got there, it's likely it came through the swamps that join up from the Howard River."

He said rangers also removed two saltwater crocodiles, one of which was 3.5 metres long, from traps in Darwin Harbour today.