Today is World Water Day, declared by the UN in 1992 and first observed the following year. Humanity could no longer drift along—we had to safeguard the very currents that keep us alive. Few places capture that urgency like Lake Tanganyika, in the Great Rift Valley of eastern Africa. From space, it"s a roughly 420‑mile ribbon linking Tanzania, Burundi, the Democratic Republic of the Congo and Zambia. At the shoreline, it"s a 10-million-year-old rift basin, formed as the Earth"s crust slowly pulled apart.