This video (by Keliotes) of the Mylopotamos river near Filotheou is made yesterday. A lot of rain is recently fallen in Greece.On the very accurate and up to date Athos map of Peter Howorth (order at http://www.filathonites.org/) the course of the river is to be seen. The bridge in the video is probably next to the U of HEOU in the left bottom corner.
In summer the river is mostly a tiny stream. Here it is, right under the (wine)house below. Next to the green rocks at the beach is the rivermouth.