Small-scale fisheries represent an important sector for Tanzania’s economy and the contribution to the livelihood of people. In Lake Babati, fish stocks are decreasing, mainly because of illegal fishing methods. This study therefore aims at examining how the problems of illegal fishing affect the fishermen, as well as their perceptions of the implemented fish ban. By using semi-structured interviews, a seasonal calendar and a Venn diagram, the data was analysed through a Critical Institutionalist lens. The results show that the fish ban has not improved the situation and that the fisheries co-management in Lake Babati is weakly practiced. Furthermore, the complexity of socially embedded relations constrains the organisation among the fishermen. As a response to the inadequate management, the fishermen suggest other solutions for preventing illegal fishing.