Catherine, from Witney, Oxfordshire, has been travelling since September last year and was reported missing on March 5.
The 23-year-old had been staying in the Lake Atitlan area of the central American country and was last seen by a friend the previous night.
The Lucie Blackman Trust, which is supporting Ms Shaw’s family, said on Monday evening that a body had been found which is believed to be Ms Shaw’s.
In a statement it added: “The Lucie Blackman Trust is saddened to announce that a body has been found in the search for Catherine Shaw.
“Formal identification has not taken place but the body is believed to be Catherine. Catherine’s family have been informed. Please respect their privacy at this difficult time.”
The charity said Ms Shaw had left the Eco Hotel in Mayachik, near San Pedro and San Juan, on March 5 at 1.37am, but then returned at 3.19am.
She then left again for the last time at 5.23am, heading in the direction of the lake.
The trust said that at this point she had a puppy with her but no other possessions.
The puppy was later found alone, shivering at the highest lookout of Indian Nose, a volcano overlooking Lake Atitlan, San Pedro and San Juan between 5am and 6am on Friday morning, the trust said.
A hand drum, known as a hang, previously reported to be in Ms Shaw’s possession, was left behind and has been located, and she did not have a guitar with her when she left, the trust added.
It has also been confirmed that she did not have a tattoo on her ribs.
The search encountered many challenges including communication issues due to lack of power in the area.