The problem of over-exploitation of fisheries resources and the attendant human activities such as beach seining, logging and farming has negatively affected fish diversity and number especially in open lagoon systems. There is dearth of information on the impact of human activities on the lagoon and fish diversity of Ogun waterside Local Government Area, Nigeria. This study assesses the fish resources and diversity as affected by social and economic activities of the people. Use of improper fishing gears depleted fish resources and consequently resulted in low income among the people. Fishing gears need to be monitored to enhance sustainability of fish diversity.