Sivasagar is situated in the fertile Brahmaputra Valley of Upper Assam. The city is defined by its incredibly lush, verdant landscapes, heavily influenced by the alluvial soils deposited by the Brahmaputra River and its tributaries.
The Dikhow River, a tributary of the Brahmaputra, flows close to the city, adding to the region's rich riparian ecosystem. The geography outside the immediate urban center is dominated by sprawling tea estates, wetlands, and scattered patches of deciduous forests. Nearby lies the Pani Dihing Wildlife Sanctuary, a rich wetland ecosystem that serves as a vital habitat for migratory birds.