The Site is a large open steep-sided lake fringed by numerous habitats such as fens, reedbeds, freshwater marsh, calcareous grassland, woodland, cutover bog and drainage ditches. There are several islands on the lake covered with deciduous woodland. Lough Ennell is of significance as a highly productive lake; its rich variety of habitats support a variety of invertebrate species and a specialist and diverse aquatic flora dominated by rare stoneworts (Chara denudata and Chara tomentosa). The Site is also important for migratory populations of pochard, tufted duck and coot, while the population of mute swan (Cygnus olor) exceeds more than one per cent of the bioregional population. Lough Ennell supports the white-clawed crayfish (Austropotamobius pallipes), as well as one of the largest stocks of wild brown trout (Salmo trutta) ever noted in an Irish fishery. It is much used for swimming, fishing, shooting, watersports, boating and camping. The inflow of effluent from the Mullingar sewage treatment plant has a significant impact on the water quality of the lake, with the ecological threat indicated by the fluctuating levels of planktonic algal growth.