Jaffna is situated on the Jaffna Peninsula, the northernmost region of the island of Sri Lanka. The peninsula is almost completely surrounded by water—the Indian Ocean, the Palk Strait, and the Gulf of Mannar—and is connected to the rest of the island by a narrow strip of land known as the Elephant Pass.
Unlike the mountainous interior of southern Sri Lanka, Jaffna's geography is characterized by its stark, flat landscape. The underlying geology is predominantly Miocene limestone, which heavily influences the region's hydrology. The peninsula is punctuated by numerous shallow, brackish lagoons, the largest being the Jaffna Lagoon. Due to the lack of major rivers, the region relies entirely on monsoon rains and underground aquifers stored within the porous limestone for its fresh water supply.