Castel Bay is a remote, expansive saltwater bay located on the northern coast of Banks Island within the Inuvialuit Settlement Region of Canada's Northwest Territories. It forms the estuarine mouth of the Thomsen River where it meets M'Clure Strait, part of the Arctic Ocean. The area is characterized by a dynamic coastal zone with brackish water habitats, gravel bars at the bay's mouth, and is situated within the protected boundaries of Aulavik National Park. This is a pristine Arctic marine environment where fishing is intertwined with significant wildlife habitat and stringent conservation protections.