Six people were rescued from the cold, choppy Magothy River on Sunday evening after their small boat was swamped with waves and sank, police said.
Two couples and two children were headed back to shore after spending the afternoon on Dobbins Island, when their 16-foot open boat started taking on water from three-foot waves, said Candus Thomson, a spokeswoman for the Maryland Natural Resources Police.
Three of the adults and the children abandoned the sinking boat and swam back to Dobbins Island. One man, who had an injured shoulder, hung onto the boat's swim ladder, Thomson said.
A father and son who were about to eat dinner on their own sailboat heard shouts coming from Dobbins and picked up a woman and her two children. They were heading back to the sinking boat when a Natural Resources Police officer on patrol in the area arrived, having heard a distress call over the radio, Thomson said.
The police officer helped get the man from the sinking boat onto the father and son's sailboat. Then the officer went to Dobbins Island to retrieve the other couple, who were on the southern side of the island, pinned up against a cliff by crashing waves, Thomson said.
The officer pulled them over the bow and into the boat, and covered the shivering couple with his boat canvas, Thomson said.
The Anne Arundel County Fire Department, Annapolis Fire Department and Coast Guard all eventually responded, and all six passengers from the sinking boat were taken to shore.
The man who had clung to the swim ladder was treated and released from Baltimore Washington Medical Center, Thomson said.
Thomson praised the father-and-son duo for helping with the rescue. They were identified as father James N. Roberts of Wyoming and son James A. Roberts of Pasadena.
"Our hats are off to the good Samaritans for doing the right thing, for being there, for having the right equipment," she said. "Awesome job by them."