The south side of Boundary Bald Mountain drains via Churchill Stream, Upper Churchill Stream, and Heald Stream (east to west) into the Moose River, then into the Kennebec River, and into the Gulf of Maine.
Drainage from the south side of Boundary Bald Mountain flows through Churchill Stream, Upper Churchill Stream, and Heald Stream (from east to west), eventually reaching the Moose River, which merges with the Kennebec River before entering the Gulf of Maine.