Lake Piso is not quite freshwater and not quite sea. It is brackish - a mingling of the two - because a single narrow inlet links the lagoon to the Atlantic, letting the ocean's tides breathe in and out across its surface. Rivers feed it from the land side: Mole Creek, the Mafa, and others draining the hills of Grand Cape Mount County empty their freshwater into the salt. The lagoon hugs the Cape Mount peninsula, the spit of land that carries the town of Robertsport on its seaward edge. The result is a shifting, in-between place, rich enough in life to support fishing villages along its shores and, beneath the rivers that feed it, something far harder than water - high-quality diamonds, washed down from igneous rock and trapped in the riverbeds.

During the Second World War, the quiet lagoon found an unlikely role. Its broad, sheltered surface made an ideal landing strip for aircraft that needed no runway, and Lake Piso became a base for Allied seaplanes - flying boats setting down on water that had known only fishing canoes. The war moved on, the seaplanes left, and the lagoon returned to the birds. In 1999 a nature reserve was established here, and in 2003 the Lake Piso wetlands - some 76,000 hectares of water, marsh, and mangrove - had become Liberia's first and only Ramsar site, a wetland recognized worldwide for the life it shelters. It remains an Important Bird Area, the pigeons of its name joined by countless other species drawn to the meeting of river and sea.

Water this useful is also water that can turn. On the nights of December 13 and 14, 2002, an overcrowded wooden ferry named the Papa Friends 2000 was crossing the lagoon near the mouth of the Mafa River. Aboard were roughly 200 people, most of them returning from the funeral of a local footballer - a community gathered in grief and now gathered, by terrible chance, in one fragile boat. The ferry capsized in the dark. Only 15 people were pulled from the water alive. The rest drowned. The lagoon that fed the villages and welcomed the seaplanes had, in a single night, swallowed a town's worth of mourners on their way home from saying goodbye to one of their own.

The land around Lake Piso is Vai country, and has been for generations. The Vai are remembered far beyond Liberia for an extraordinary achievement: in the early nineteenth century, one of them, Momolu Duwalu Bukele, developed a writing system - a syllabary of their own design, one of the few indigenous scripts created in Africa in modern times. To live beside Lake Piso is to live in a place layered with meaning: a lagoon named by people who read the sky for pigeons, who built their own letters, and who still cast their nets where the rivers run into the tide. The water keeps its rhythm, in and out with the Atlantic, indifferent and essential, the heart of a corner of Liberia that the wider world rarely sees.