Lake Tana has played an important role as a major livelihood source for many households, and contributed as a protein source by its fish stock. However, in Lake Tana, overfishing is the biggest problem that results from fish resources being exploited above their optimal amounts. Therefore, the study aimed to determine optimal allocation of fish stock in the lake and possibly identify major determinants of overfishing. To achieve the objectives of the study, A bioeconomic model was employed to predict or determine the optimal points (Maximum sustainable yield, maximum economic yield, open access yield, Effort of Maximum economic yield, effort of Maximum economic yield, and effort open access yield), and a Tobit model was also employed to identify determinants of over-fishing associated with CPUE. The Focus Group Discussion and Key Informant Interview were also employed to deal with some management options, possible solutions, provide justifications, and other important qualitative evidence. Household survey data were gathered using a multi-stage sample technical approach, utilizing cross-sectional data and three-year secondary fish stock data from BFALRC. As the study result shows, most fishers are practicing catch (fishing) above optimal points in each type of fish species. The MSY amount for Labeobarbus species, Nile Tilapia, and catfish were 534763.2 Kg, 534,645 kg, and 547600 kg, respectively, while MEY points are 356, 533.6 kg, 527,891.46 kg, and 438,369.75kg for Labeobarbus species, Nile Tilapia, and catfish, respectively. Among determinants of overfishing, adult equivalent, educational status, training, active fishing days, own total land, and the number of monofilament gillnets have a significant and positive effect on overfishing. Boat type, fishing experience, and TLU are negative and significant determinants of overfishing associated with Catch per unit effort. Therefore, refining (re - vised) the fishing rules and regulations of the Lake Tan fish resource management on major factors of overfishing can maintain the sustainability of fish stock in a lake for upcoming generations. Creating wide awareness, providing tentative training, developing seasonal income strategies, restricting the mesh size and type of gill nets, enforcing regulations on closed season fishing, and limiting the quantity and number of gill nets are possible solutions to resolve the overfishing problem. Therefore, policies, rules, and regulations of governmental interventions should be implemented to address and close the gaps in the lake.