Before the update on 25 February2009, river trolls were a random event that occurred while a player was fishing. These NPC monsters would appear and attack players when the player initially made an attempt to fish. They would say " Fishes be mine!" before attacking the player. The river troll's combat level used to vary depending on that of the player's, up to a maximum of level 159. Like most other random events at the time, the river troll could be fled from, as it only had a Melee attack.
Despite their name "river troll", they would appear even if the player was fishing in the sea.
This statement explains the possible origins of the River troll, as taken from Postbag from the Hedge; "Dem fishes be mostly in de river. Den big trollnado come. Me and Dem missus in Dem whirlpool, get into Dem sea. Me’s get in Dem big trouble. Me hear Dem trolley get us back to Trollheim. Me’s try eating that clown fish, but it taste funny to me. If you’s helping Dem trolls get home, me gives big trollipop! Maybe."
Like all trolls, it received a graphical update during March 2011.