Masri reservoir is, unlike the Cap Bon reservoirs, being constructed for water-supply to the national grid rather than local irrigation. It is situated quite high up in the Dorsale and flanked by mountains which reach 660 m, to the west of the town of Grombalia, south-east of Tunis. The shores are lined with vegetation composed mainly of Phragmites communis, Typha angustifolia and Juncus species. The mountain slopes are clothed in a forest of Tetraclinis articulata.
See Box for key species. Though the reservoir is small, it holds Oxyura leucocephala (10–50 pairs), while breeding species include Podiceps cristatus and Tachybaptus ruficollis. Wintering waterbirds include Aythya ferina and Fulica atra.
Non-bird biodiversity: The mammal Hyaena hyaena (LR/nt) has been recorded from the mountains around the site.