Le Grau-du-Roi is south of Aigues-Mortes, in the Gard department. It is in the
canton of Aigues-Mortes. It is separated from Aigues-Mortes by a series of saline marshes, called
étangs in French, and a bend in the river
Vidourle. The
étangs are named as follows: l'étang du Ponant, l'étang du Médard, l'étang du Repausset Levant, and the lac de Salonique, which is a lake rather than a marsh, as its name suggests. To the west of the town, the coastal strip is breached where the
Vidourle empties into the Mediterranean, and to the east is that of the
Petit Rhone. The course of these two rivers has been subject to change and reversal. The Rhone used to flow into the
étangs further to the west and at one point, the Vidourle flowed into it rather than the sea, The route in the 12th century was through the Grau Louis and the Old Channel. In 1570, a new breach occurred at a point called Gagne-Petit. It is around this grau that the settlement was formed. The area between the
étangs and the sea was settled by Italian immigrants at the end of the 19th century. From then until the 1920s, the economy was based entirely on fishing, but tourism later became important, culminating in the construction of Port-Camargue.
Le Grau-du-Roi station has rail connections to Nîmes. The modern-day resort town benefits from 18 km of fine sand beaches, with sand dunes on the Pointe de Éspiguette forming an important wildlife habitat. The
étangs are noted for their birds, which include
flamingoes.
Climate Le Grau-du-Roi has a
hot-summer Mediterranean climate (
Köppen climate classification Csa). The average annual temperature in Le Grau-du-Roi is . The average annual rainfall is with October as the wettest month. The temperatures are highest on average in July, at around , and lowest in January, at around . The highest temperature ever recorded in Le Grau-du-Roi was on 16 August 1987; the coldest temperature ever recorded was on 12 January 1987. {{Weather box|width=auto == History ==