An island in the far Western Sea, Green Isle was inhabited by otterclans for many seasons. However, they were conquered by wildcat invaders from the south, and enslaved. Their last great ruler was High Rhulain Gennia Wildlough. The last Wildcat Warlord of Green Isle, Riggu Felis, was challenged by a band of otter rebels led by Leatho Shellhound. The Feral-Cat army of Green Isle was eventually defeated, and Tiria Wildlough of Redwall Abbey became the queen of a peaceful Green Isle.

Green Isle has a mixed geography. To the north is a beautiful vale, Holt Summerdell,  which was once a favorite resort for the otters before the wildcat invasion. Summerdell became the clans' permanent home after the war.

The central part of the island is dominated by a huge lake, Deeplough , where the legendary monster Slothunog used to reside before its death at the paws of Cuthbert Blanedale Frunk. The great pine fortress of Green Isle, once ruled by otters, was to the south, but dominated by the wildcats after the conquest. This fortress was burned in the war where Felis was defeated.

Green Isle appears in "High Rhulain" in canon.

Green Isle faced danger again when Vilaya's Incompetents came to the Isle after the cubs. Tiria willingly exchanged herself for the cubs.