Fenris Isle is a large island located in the center of Lordamere Lake. The island is generally considered to be a part of Silverpine Forest, and together with the Dawning Isles, form a broken circle of dry land in the lake. This formation was once the rip of an ancient volcano, long since eroded down by the elements.
Fenris Isle was once home to a thriving military outpost of the Kingdom of Lordaeron called Fenris Keep, ruled by a promising young lord who frequently traded goods via ferry with the Silverpine mainland. When the Undead Scourge took the land, Fenris Isle was abandoned, all of its inhabitants either fled or murdered.
The island was then occupied by the Rot Hide gnolls, who had taken the keep as their base of operations. The Rot Hides were led by their treacherous master, Thule Ravenclaw, who has taken complete control of the island and the nearby Decrepit Ferry. However, they too were run off from the island as Hillsbrad Refugees made their way here from Southshore and Hillsbrad Fields.
These survivors of the Forsaken attacks would live in peace but for a moment, as agents of the Forsaken along with Agatha entered the island and began killing them and raising them into the undead. Darius Crowley made them an offer they couldn't refuse, either die and join the ranks of the undead, or drink his blood and become a worgen and continue to fight for the Alliance. They choose vengeance and became Hillsbrad Worgen.
Following the Battle for Lordaeron, Fenris Keep was fought over between the Bloodfang Pack worgen and the Forsaken led by Deathstalker Hayward. The Bloodfang eventually came to control the island, forcing the Forsaken to divert their attention so they could evacuate the refugees across the lake safely. Fenris Isle is now one of two strongholds used by the Bloodfang Pack to keep a watch over Silverpine Forest, in addition to Shadowfang Keep.