State Region 4 Marine Police Commander ACP Mohamad Madun said the first arrest was made when police spotted seven people on board a vessel, which was slowly moving towards the riverbank at about 6.45am.
"The passengers, including the skipper, were detained when they failed to produce identification documents," he said.
He said a total of nine people on board a vessel which was also heading the same direction at about 7.10am were also arrested when they too failed to produce identification documents.
"The detainees, comprising 11 men and five women, were brought to the marine base here to facilitate investigations and referred to the Immigration Department," he said, adding the boats and Yamaha engines worth about RM39,000 were also seized.
Mohamad said this was the second such case within two months.