Bockarie Sonnah, 14, died on Monday evening at the Torduff reservoir in Colinton, Edinburgh.
Yesterday a message written by the McIntosh family said: "If only you knew how much we love you and are heartbroken we have lost you."
The flowers and card were placed at the reservoir by his foster father, Derek, and a boy believed to be his son, Michael.
Both men looked upset as they read other tributes and messages that had been left.
As they walked down to the site, neither of the two spoke to each other and left quietly. The family's message read: "Bockarie, Thank you for being part of our family and giving us a wonderful, happy two and a half years. If you only knew how much we love you and are heartbroken we have lost you.
"We will never forget you son as you will always be in our hearts and memories forever.
"All our love, Derek, Sharon, Michael, Kayleigh and Millie."
Bockarie died on Monday night after swimming at the reservoir with friends.
It is believed he was going for one last jump from a 10ft valve tower when he began struggling in the water at about 6.15pm.
Despite efforts by emergency services to save Bockarie, his body was recovered from the water at around 10pm.
The teenager played for football club Redhall Star YFC 2000s. In a statement on its website the club said he was a "huge presence who would light up the room with his huge smile and bouncy personality".