This study was designed to investigate the effects of methods of processing (such as smoking, salting and sun-drying), location, species and seasonal variations on the levels of four toxic heavy metals namely lead, cadmium, mercury and arsenic in edible muscles of four local freshwater fish species namely Tilapia nilotica (Tilapia), Synodontis guntheri (Kurungu), Heterotis niloticus (Bargi), and Clarias anguillaris (Catfish), collected from Alua Dam, Doronbaga and Daban Masara within the Lake Chad Basin of Borno State, Nigeria. The fish and the corresponding water samples were collected directly from the fishing sites in the three locations during the dry season (September 2009 to March 2010) and the rainy season (May to August 2010). Samples were transported from sites to the Food Science Laboratory, University of Maiduguri, inside previously cleaned insulated plastic coolers (100 liters capacity) containing ice blocks, where they were sorted by location, species, and size. An average of 4 - 5 matured fish was used for each of the treatments per location. The samples were wet-digested overnight in mixtures of concentrated nitric and sulphuric acids in the ratio of 2:1...