Ice Mountain Lake is an unofficial name given to an inland body of water featured in the first RuneScape novel, Betrayal at Falador. The lake itself cannot be found in-game, although the book suggests that it is located approximately 30 miles east of Ice Mountain's base. According to the novel, the lake is formed by runoff from the peaks of Ice Mountain. The lake is described as being clear, still, and thus it presumably lacks major currents. It houses a huge number of silver fish, which are apparently edible.
In the novel, Squire Theodore, Arisha, Castimir, Ebenezer, Gar'rth, Doric, and Kara-Meir camp near the lake on their way to the Monastery of Saradomin near Asgarnia's northern border. After Castimir and Theodore fail to catch any fish through conventional methods, Ebenezer throws a canister of oil and sodium into the lake, causing an explosion that stuns several fish, allowing for their easy capture.
The lake itself cannot be found in-game, suggesting either that it no longer exists (possibly due to the mountain's recent climate changes) or that it is simply not shown due to Scale Theory.