Seward Mountain stands within the watershed of the Raquette River, which drains into the Saint Lawrence River in Canada, and into the Gulf of Saint Lawrence. The southeast slopes of Seward Mtn. drain into Seward Brook, thence into the Cold River, a tributary of the Raquette River. The west end of Seward Mtn. drains into Calkins Brook, thence into the Raquette River. The northern slopes of Seward drain into Ward Brook, thence into Ampersand Lake, Ampersand Brook, Stony Creek, and the Raquette River.