Lake Victoria fishery activities are of crucial economic importance to the communities around East Africa as they support the majority of fishers specifically through Nile perch fishing. As a consequence, increasing fishing pressure had also led to overfishing. This study employed the Data Envelopment Analysis (DEA) and Propensity Score Matching (PSM) techniques to assess the impact of Nile perch overfishing on technical efficiency of fishers based on a survey of 268 fishers across 10 landing sites in Lake Victoria, Tanzania. Results from the DEA show that, overall Nile perch fishers have average technical efficiency of 30% which indicates a high level of inefficiency. Specifically, there is no statistically significant difference in the technical efficiencies for Nile perch fishers who are overfishing and those who are not overfishing due to fisher’s mobility across the Lake. In addition, mode of propulsion and being a member of fishery organization were found to be statistically significant factors influencing inefficiency of Nile perch fishers. Furthermore, results from the probit estimates of the PSM show that being a member of fishery organization, quantity of Nile perch harvested per trip, age of a fishing vessel (boat), the gillnet mesh size and cost of fishing inputs have statistically significant effect in influencing the probability of Nile perch overfishing. However, further result indicates that Nile perch overfishing do not have statistically significant impact on fisher’s technical efficiency. Therefore, this study recommends a need to monitor and formalize fisher’s mobility as one of the alternative for co-management of the Lake. Also, overfishing can be controlled without necessarily affecting technical efficiency of Nile perch fishers through training and access to proper fishing gears.