As the Niger Delta is a major crude oil exploration region with no stringent environmental laws in Nigeria, the ecological risk assessment of heavy metals in mangrove sediments is critical due to their persistence and toxicity. This study analyses the concentrations of five different heavy metals, which included cadmium, lead, copper, nickel, and zinc, in mangrove sediments of the Buguma community, Asari-Toru Local Government Area, in the Niger Delta, applying ecological risk indices to determine the contaminations and ecological threats of heavy metal pollution. Samples were collected from three different sites. Site 1: located near a sediment heap, a dump site with oil sheen, litter, and particulate contaminants, with an old local illegal crude oil refinery; site 2: an area with maritime discharges, sewage, and commercial wastes dumped nearby; and site 3: a densely populated settlement lining the tidal-swept mangrove swamp with household pollution. The research was carried out by employing ecological risk indices, which included the Contamination Factor, Degree of Contamination, Ecological Risk, Potential Ecological Risk, Pollution Load Index, and Enrichment Factor. The results showed that arsenic and lead exceeded human permissible limits, while cadmium, zinc, and nickel were within limits. The ecological risk assessment indices revealed that the sediments have varying levels of heavy metal concentration. The applied ecological risk indices were as follows: Ecological Risk: Cu (high ecological risk) and Pb (very high ecological risk); Enrichment Factor: Cd, Zn, and Pb; Degree of Contamination (very high degree); Contamination Factor: Pb (moderately degree) and Cu (high degree); and Potential Ecological Risk (obviously high). The results indicated increased levels of the heavy metals in all the sediments, indicating health and ecological risks to humans and aquatic biota, linked to anthropogenic activities. The results recommend efficient governance strategies and strict policy interventions for the immediate remediation of these sites. The results also suggest that further research should be conducted on the histopathological and biochemical effects on humans and benthic organisms.