Upcoming Rift Scuttler changes.
It seems like Riot is going to alter Rift Scuttler in the upcoming patches, so that there is only 1 spawning randomly in the river, rather than 1 in each side and it will start spawning at 1.40, rather than 2.15.
Watch out for those level 1 deathbrawls for Rift control, since it will apparently grant a big amount of xp and gold if claimed.