Réserve naturelle nationale du Mas Larrieu, National nature reserve in Argelès-sur-Mer and Elne, France

The Réserve naturelle nationale du Mas Larrieu is a 145-hectare triangular reserve around the mouth of the Tech, shared by Argelès-sur-Mer and Elne. It holds three main environments: beaches with mobile and fixed dunes, reed beds of Provence cane along the river, and riparian forest with 42 woody species. Its highest point is 12 metres.

The reserve was created by a decree of 17 July 1984, covering 145 hectares on both banks of the Tech mouth in the communes of Argelès-sur-Mer and Elne. Its perimeter runs from the former bed of the Tech in the north to the grau de la Riberette in the south, reaching a maximum altitude of 12 m. It is managed by the Fédération des réserves naturelles catalanes together with the commune of Argelès-sur-Mer.

The reserve's name comes from the Mas Larrieu, a former farmstead on the site. Today the main public use is the beach at the Tech mouth, where swimming and seaside leisure draw visitors from Argelès-sur-Mer. The reserve is managed by the Fédération des réserves naturelles catalanes together with the commune of Argelès-sur-Mer.

The reserve lies on both sides of the Tech mouth, between Argelès-sur-Mer and Elne, and is reached from the beach car parks of Argelès. The main draw for most visitors is the beach, and the site is managed by the Fédération des réserves naturelles catalanes with the Argelès-sur-Mer municipality. The highest point is only 12 m, so the terrain stays flat and easy to walk.

The reserve protects one of the last natural river mouths along the Roussillon coast, where fresh and salt water meet in an undisturbed state. This rare mixing zone creates conditions found nowhere else in the surrounding region.