Diarrheal disorders significantly contribute to child morbidity and mortality in vulnerable populations such as fishing communities. This study aimed to determine the prevalence of diarrheal disorders among under-five children and to identify the behavioral and environmental risk factors associated with diarrhea using Social Cognitive Theory (SCT). Additionally, the study explored feasible action points to mitigate these adverse factors. A community-based, explanatory sequential mixed-methods study was conducted in four fishing villages of Karaikal, India. The study included a cross-sectional survey of 155 households, followed by environmental surveillance and focus group discussions (FGDs). Data were collected using structured questionnaires, observational checklists, and water and food quality assessments. Quantitative data were analyzed using logistic regression models, while thematic content analysis was applied to qualitative findings. The prevalence of diarrhea among under-five children was 30.3%. Key behavioral and environmental factors associated with diarrheal disorders included unawareness, uncovered cooked foods, and poor sanitation practices. Additionally, chemical and bacterial contamination of drinking water and food adulteration were prevalent. FGDs identified multiple-intervention strategies, including handwashing promotion, sanitation improvements, and enhanced healthcare access. The findings of this study would help in the development of key messages for designing context-specific behavior change communication interventions.