Green tree frogs and red-back spiders may occasionally call your toilet home, but have you ever wondered what else might lurk underneath the seat?

With the dry season, crocodiles search for a home outside of major swimming holes, and Darwin's sewerage system appears to be quite inviting.

Skefos Tsoukalis from Power and Water said the reptiles had been sneaking into the system for at least a decade.

"I have seen a croc sunbathing at our Katherine sewage pond.

"We do have crocodile traps in all of our ponds and we are working [with Parks and Wildlife] to remove them from our systems."

Traps are used to catch crocs that venture into the system. (File photo) ( Supplied: NT Parks and Wildlife )

Mr Tsoukalis was pretty relaxed about the situation — at least it's nothing like the plot of Hollywood movie Alligator.

The 1980s flick involved the title character surviving in the sewers of Chicago by eating discarded lab rats pumped with growth hormones.

"Although I did watch that film when I was growing up, here the crocodiles are crawling up through our [pond] fence or through our outfall which discharges into the mangroves," he said.

"We don't have CCTV cameras in our pipes so we cannot accurately detect when they come in."

Is it safe to lift the seat?

Mr Tsoukalis said Power and Water managed the problem as best it could.

"Our number-one priority is safety, safety for our team members and obviously for the public.

"There will be no snappy endings in your toilets.

"Because of the size of the pipework, and we have infrastructure that separates our treatment facilities from the ponds, it's very difficult for them to swim upstream."

Mr Tsoukalis said he would not be adding croc wrangler to his CV anytime soon, but explained that even the sewerage system provided a diverse ecosystem for local species.

"There are fish in our sewage ponds — and birds, these systems are like a food bowl for wildlife."