Laguna de Términos is the largest tidal lagoon by volume located entirely on the Gulf of Mexico, as well as one of the most biodiverse. Exchanging water with several rivers and lagoons, the Laguna is part of the most important hydrographic river basin in Mexico. It is important commercially, as well as ecologically by serving as a refuge for an extensive number of flora and fauna; its mangroves provide an important role as a refuge for migratory birds. Geography Laguna de Términos (Lagoon of Ends, as it is the end of regional rivers) is made up of a series of rich, sediment-laden lagoons and tidal estuaries connected by two channels to the Bay of Campeche in the southern part of the Gulf of Mexico. It lies in the southwestern part of the Mexican state of Campeche, mostly within Carmen Municipality, with the southwestern portion in Palizada Municipality. It is long, wide, and covers an area of . Every nine days, approximately 50% of the lagoon's water volume is renewed, primarily through the effect of ocean tides. Isla del Carmen is a barrier island which separates the lagoon from the Bay of Campeche. There are two permanent channels connecting the lagoon to the Bay of Campeche – Boca de Puerto Real to the east of Isla del Carmen, and Boca del Carmen to the west. Inflow from the bay is via the Boca de Puerto Real, and outflow is via the Boca del Carmen. Its shores are swampy and support extensive mangroves. It is fed by several freshwater rivers, which empty into the main lagoon via smaller lagoons. The Candelaria River enters from the southeast via Panlao lagoon. The Chumpan River enters from the south via Balchacah lagoon. Two distributaries of the Usumacinta River flow into the western lagoon – the Palizada River enters via Viento Este and Vapor lagoons, and the San Pedro y San Pablo River flows into a chain of lagoons, including Pom and Atasta, west of and connected to the main lagoon.<ref name = Nooren>Kees Nooren et al. (2017). The Usumacinta–Grijalva beach-ridge plain in southern Mexico: a high-resolution archive of river discharge and precipitation. Earth Surface Dynamics, 5, 529–556, 2017 https://doi.org/10.5194/esurf-5-529-2017</ref> The Palizada provides about 75% of the total freshwater inflow to the lagoon, and the western end is generally more nutrient-rich and less saline than the eastern end. The city of Ciudad del Carmen is located