The grey-blue waters of the Eastern Sea are populated by fierce carnivorous sea gulls and a big fish. The Pigmy Shrew Caves are located along the sea, and the Broadstream River feeds it further south.
Martin the Warrior, Rose, Grumm Trencher, Felldoh and Brome took to the Eastern Sea in one of Clogg's damaged small boats during their escape from Fort Marshank. When their boat finally sank, the fugitives were forced back to the shores of the Eastern Coast further north than Marshank.
The Eastern Sea is mentioned in Martin the Warrior.