Environmental disasters, such as the Flint, Michigan, water crisis, are potentially traumatic events (PTEs) that may precipitate long-term psychiatric disorders. The water crisis was associated with acute elevations in mental health problems in the Flint community, but long-term psychiatric sequelae have not yet been evaluated using standardized diagnostic measures. To investigate the prevalence of and factors associated with current presumptive diagnostic-level major depression and posttraumatic stress disorder (PTSD) among Flint residents 5 years after the onset of the crisis. In this cross-sectional study, a household probability sample of 1970 adults living in Flint, Michigan, during the crisis were surveyed about their crisis experiences, their psychological symptoms 5 years later, and their access to and use of mental health services in the intervening years. Analyses were weighted to produce population-representative estimates. Presumptive Diagnostic and Statistical Manual of Mental Disorders (Fifth Edition) (DSM-5) diagnostic-level past-year major depression and PTSD. Among 1970 respondents, 1061 of 1946 reporting sex (54.5%) were women; 1043 of 1951 reporting race (53.5%) were Black or African American and 829 (42.5%) were White; and 1895 of 1946 reporting ethnicity (97.4%) were non-Hispanic. Overall, 435 (22.1%) met DSM-5 criteria for presumptive past-year depression, 480 (24.4%) for presumptive past-year PTSD, and 276 (14.0%) for both disorders. Residents who believed that their or their family's health was harmed by contaminated water (eg, risk ratio [RR] for depression: 2.23; 95% CI, 1.80-2.76), who had low confidence in public-official information (eg, RR for PTSD, 1.44; 95% CI, 1.16-1.78), who had previous exposure to PTEs (eg, RR for both disorders: 5.06; 95% CI, 2.99-8.58), or who reported low social support (eg, RR for PTSD, 2.58; 95% CI, 1.94-3.43) had significantly higher risk for depression, PTSD, and comorbidity. PTEs involving prior physical or sexual assault were especially potent risk factors (eg, both disorders: RR, 7.30; 95% CI, 4.30-12.42). Only 685 respondents (34.8%) were ever offered mental health services to assist with water-crisis-related psychiatric symptoms; most (543 [79.3%]) who were offered services utilized them. In this cross-sectional study of psychiatric disorder in Flint, Michigan, presumptive depression and PTSD were highly prevalent 5 years after the onset of the water crisis. These findings suggest that public-works environmental disasters have large-scale, long-term psychological sequelae. The Flint community may require expanded mental health services to meet continued psychiatric need. National disaster preparedness and response programs should consider psychiatric outcomes.