The 17-year-old from Waitepeka, near Balclutha, and his father Paul (48) spent six days paddling the length of the Clutha River, before taking on the sea to reach Kaka Point.
Although slightly behind schedule, the fundraising trip was without mishap apart from an icy plunge for Mr Richardson on Sunday.
Sam completed the second-last leg from Balclutha to the river mouth solo, after Mr Richardson left the water just north of Balclutha, and was joined by an IRB manned by members of the Kaka Point Surf Life Saving Club as he paddled from the river mouth to Kaka Point.
"That'll do me for a wee while, but I'll definitely jump back in it," a tired Sam told the Otago Daily Times yesterday.
The worst part of the river journey was at Lake Roxburgh where strong headwinds made paddling tough, he said.
Sam was looking forward to "a good sleep" last night.
The trip was inspired by the McGlashan Challenge, a voluntary challenge of Dunedin's John McGlashan College, which Sam attends.
Senior pupils set themselves a challenge of their choice, and for keen Kaka Point Surf Life Saving Club members Mr Richardson and Sam, tackling the mighty Clutha River on surf skis was an obvious choice.
Mr Richardson said he was "immensely proud" of his son.
Sam's mother Paula and sister Olivia were on hand throughout the journey as support crew.
As of last night, Sam had raised more than $1300 for his chosen charity, the Otago Community Hospice, which supported his grandfather when he was ill two years ago.
