Tuyutí (), "white mud" in guaraní, is a marsh with a pond located in the southwest corner of Paraguay. It became famous during the Paraguayan War, while the allied army bivouacked on it for two years. The Battle of Tuyutí in 1866 was the biggest battle ever fought in South America and the deadliest day in the Americas history. The smaller Second Battle of Tuyutí was also fought there.