Northern Territory Police say an officer had to jump into a crocodile-infested river to save a man trying to escape arrest.

The man was stopped by traffic police at Kalkarinji, about 460 kilometres south-west of Katherine, yesterday afternoon.

He was wanted for questioning by police over an alleged domestic-violence assault.

Watch commander Garry Smith says the man fled into the Victoria River, despite being unable to swim.

"He ran to the local river and jumped in," he said.

"However, due to his lack of swimming abilities, it was probably not his best choice of escape.

"One of the local police members jumped in and conducted a dual role, namely saving him and arresting him."