Amazon river creature "torments" kayaker

[Maxmars]

A woman I went to high school with and remained friends with over the years is the Director/Curator of primates at the Bronx Zoo.  Prior to that, she was the director of Mammals there.  I asked her to look at the footage and she said "There's no way that's a manatee".  She's not sure what it is, but she said the splashing at a distance near the end of the video was interesting and more indicative of a reptile or school of fish than a mammal.

Very cool.  I am surprised because I thought the 'flipper-like' or perhaps 'fin' rolling out of the water, that was my best guess.  Of course I defer to experienced experts... so now the question resurfaces ( pun) ... what was it?