The existing Guinness World Record, set in 2006, stands at 326.98 miles – but Skelton has clocked up more than 1,000 miles in just three weeks as she battles through her adventure.
Organisers say the plucky 26-year-old has also set a new Guinness World Record for the longest distance in a kayak in 24 hours by a woman by paddling her way through 75 miles of Amazonian waters in one day.
Evidence of both feats is being sent to Guinness World Records for final verification.
Helen said of her tough challenge: “One thousand miles down, one thousand miles to go. I know I’ve got a lot of hard work still to do but at least I am closer to the end than the beginning now.
“Every single day here is tough so all I can do is take each one at a time and get through it. I have been suffering with the heat, my shoulders are sore and my legs are covered in mosquito bites but I’m battling on.”
Helen set off on January 20 near Nauta in Peru, and is aiming to finish 2,010 miles downstream at Almerim in Brazil. She is paddling around 60 miles a day to reach the target in just six weeks and has just one rest day a week.
A statement from Guinness World Records said: “We hope to ratify both these records as quickly as possible to recognise this fantastic achievement”.