Windy conditions have hampered the search for a teenager missing at a lake on the Victoria-NSW border.
Two 16-year-old boys were fishing in a tinnie on Lake Mulwala at Yarrawonga about 9am on Sunday when they were hit by a wave and fell overboard, police said.
A good Samaritan swam to their aid and pulled one of the boys to shore using a flotation device.
He returned for the second boy but could not find him.
Victoria's State Emergency Service, Centre for Maritime Safety NSW, NSW Police, Victoria Police and other government search and rescue squads are working together to locate the missing boy.
Victoria Police Senior Sergeant Nathan Ractliffe said windy weather conditions had made the search difficult.
"The weather conditions today and the next couple of days aren't very favourable to assist police but we're doing everything we can in our capability to locate that male," he told reporters on Monday.
The surviving teen is said to be receiving family support after the traumatic incident and continues to help police.
Police divers and members of the Air Wing searched the lake on Sunday until about 7pm. They resumed the search at 8am on Monday.
