Rio Grande Estuary
The Rio Grande Estuary forms a natural border between the United States and Mexico and is a riverine estuary which flows directly into the Gulf of Mexico with no associated bay system. The estuarine portion of the river occurs where tides from the Gulf of Mexico mix with fresh water from the river. Annual average inflow from the Rio Grande is 370,722 acre-feet per year, but can range widely due to extreme hydrological conditions. The Rio Grande Estuary is surrounded by Cameron County on the Texas side and is located within the boundaries of the Region M (Rio Grande) Regional Water Planning Group.