Flooding is a recurrent problem in rapidly developing urban districts such as Lokogoma, Abuja, where inadequate drainage, poor land-use planning, and weak infrastructure maintenance increase flood vulnerability. This study assessed the causes, impacts, and effectiveness of existing flood mitigation measures in Lokogoma District, Abuja, Nigeria. A mixed-methods approach was adopted, involving field observation, questionnaire surveys, stakeholder interviews, secondary data review, and geographic information system (GIS)-assisted mapping. A total of 381 questionnaires were administered to residents in flood-prone residential areas, and the data were analyzed using descriptive statistics, mainly frequencies and percentages. The findings show that 79% of respondents had been affected by flooding, while 53.3% reported that flooding occurs frequently. Poor drainage conditions were identified as the leading cause of flooding, accounting for 27.6% of responses, followed by building on waterways and improper planning, each accounting for 22.0%. The major impacts of flooding included disruption of daily activities, economic loss, loss of personal belongings, health issues, property damage, and displacement from homes. Existing mitigation measures included drainage systems, sandbags/barriers, building elevation, flood walls, community education, early warning systems, vegetative barriers, land-use planning, and flood insurance. However, respondents expressed mixed views about their effectiveness, with 44.9% rating the measures as effective or very effective and 39.4% rating them as ineffective or very ineffective. The study concludes that flooding in Lokogoma is driven by inadequate drainage capacity, poor maintenance, improper waste disposal, weak development control, and limited community participation. It recommends upgrading secondary and tertiary drainage systems, improving solid waste management, enforcing land-use and building regulations, conducting regular drainage maintenance, reviewing flood risk assessments, and strengthening public awareness and community participation. These measures can enhance flood resilience and support more sustainable urban development in Lokogoma District.