Small rivers are accessible from your rental on foot. Within an hour by car you can reach the largest rivers, lakes and the sea.
Highly frequented places are
Gorges d'heric (also for boating and climbing)
https://www.laregion.fr/Les-Gorges-d-Heric
the Orb for canoeing
https://www.laregion.fr/Les-Gorges-d-Heric
Lac de Raviege for the rental of boats, canoes, sailing
A gem is the river spot at La Ribaute
The beaches of Gruissan (picturesque with its chalets, Le Grand Soleil restaurant or La Perle for seafood), Valras Plage (many play areas for children) and Cap d'Agde (Mangos beach tent!)