Rescuers from the Marshfield police and harbormaster’s office rescued four men Wednesday from a sinking boat in Plymouth Bay.

A woman called police shortly after 6 p.m. Wednesday to report that the boat her husband and sons were on had begun to take on water, according to a Marshfield police report.

The boat was near Gurnet Point Light. When the rescuers, Police Chief Phil Tavares, Officer Stephen Mulligan, and assistant harbormaster Robert Coakley, reached it, the stern was already submerged. Two passengers had freed themselves from the boat and were treading the 46-degree water. They were pulled aboard.

Anthony Gonsalves, 31, went under the water to try to rescue his father, Stanley Gonsalves, 69, from the small cabin area of the boat, police said.

“Stanley was having trouble freeing himself from the vessel due to the fact the canvas top was now at water level over him while the vessel continued to sink,’’ Mulligan wrote in his report.

After tense moments when Anthony Gonsalves was lost from sight, the rescuers were able to free Stanley from the vessel.

Tavares “was able to rip the canvas cover off the boat, freeing Stanley from the vessel. Moments after Stanley was freed from the vessel, Anthony popped up out of the water,’’ the officer wrote.

All four of the men rescued were showing early signs of hypothermia. Tavares said all four had been released from the hospital as of Thursday.

Kilgannon can be reached at maddie.kilgannon@globe. com.