Mouth of the Muga Nature · Castelló d'Empúries, Alt Empordà, Girona Image of Castelló d'Empúries, not of the place itself. The river Muga flows into the Gulf of Roses, within the municipality of Castelló d'Empúries, between Empuriabrava and the Aiguamolls de l'Empordà protected natural area. With an average flow of 3.34 m³/s at its mouth, its waters are home to grey mullet and sea bass alongside barbel, trout, river crayfish, eels, grass snakes, salamanders, toads and frogs. Silting has caused the old estuary and the medieval port known as the grau de la Muga to disappear. Photo: Alberto-g-rovi (CC BY-SA 3.0) What to see and do in Castelló d'Empúries