Contos says that he made his discovery while using Google Earth to plan some new kayaking routes in Peru. Previously it has been assumed that the Apurimac River marks the furthest starting point of the Amazon, but he believes that its true source sits on the 18,363-foot (5597 meter) Nevado Mismi mountain, where the Mantaro River begins. By Contos' estimates, the Mantaro is approximately 50 miles longer than the Apurimac, giving it the distinction of being the furthest source.
If what Contos says is true, we'll eventually have to re-write the record books on the first descent of the river. As of right now, it hasn't been done. At least not by kayak. Contos shared his findings with West Hansen, who was launching his Amazon Express expedition last year, but the two had a bit of a contentious relationship it seems, which led to Hansen going the historical route and Contos using motorboats to complete a first full descent of what he believes is the Amazon River. The Outside article has more details on the situation between the two men, which seems like it can best be described as frosty.
For now, we have to wait to see if there is independent confirmation of this new finding, which Outside speculates could lead to a rush of expedition paddlers heading to South America to attempt to become the first to run the Amazon from the "new" source to the sea. Regardless if it is proven or not however, I suspect there are some already planning to make the run, just so they can lay claim to it.