This mixed-methods study integrates quantitative parasitological surveys with qualitative knowledge, attitude and practice (KAP) assessments to evaluate trematode transmission patterns and describe human behaviour relevant to transmission among communities in hydropower reservoir areas of northern Vietnam. A total of 798 participants provided fecal samples, and 135 heads of household were interviewed. Overall, 236 individuals (29.57%) were infected with at least 1 helminth group. Fish-borne zoonotic trematodes (opisthorchiid/heterophyid-type eggs) were the predominant parasite group (22.56%), followed by soil-transmitted nematodes (Ascaris lumbricoides, Trichuris trichiura, Ancylostoma/Necator spp.) (7.14%), tapeworms (Taenia sp.) (0.63%) and pinworms (Enterobius vermicularis) (0.13%). The prevalence and intensity of trematode infections were higher in men than in women. Infection levels were higher in older age groups, whereas infection in children (<16 years) was low. Marked spatial heterogeneity was observed among reservoirs. KAP surveys revealed limited understanding of trematode transmission routes, despite prior health education efforts. A pervasive misconception was that wild-caught fish or home-raised animals are safe to consume raw. Sanitation remained inadequate, and 73.33% of interviewees reported treating sick animals without veterinary consultation. Regular anthelmintic use was rare, with only 10.37% of interviewees reporting that they dewormed themselves twice per year, as recommended. These findings suggest hydropower reservoir regions in northern Vietnam may represent potential hotspots for food-borne trematode transmission. The observed patterns may indicate ongoing transmission, with ecological conditions and cultural practices as possible contributing factors. Targeted One Health–based interventions integrating human, animal and environmental health are recommended.