The effects of local environmental conditions on the regional distribution, prevalence, and infection intensity of Ergasilus labracis (Copepoda) parasitic on 3-spined stickleback (Gasterosteus aculeatus) was investigated in the Bay d'Espoir region of Newfoundland during May to September of 2015. Environmental conditions (e.g., temperature, salinity, and oxygen) were measured monthly at 7 beach sites distributed through the region. Analysis of environmental characteristics indicated that the area could be divided into 3 zones based on salinity (low-salinity zone: 13.56 ± 0.32 practical salinity units [psu]; medium-salinity zone: 21.11 ± 0.04 psu; high-salinity zone: 29.91 ± 0.32 psu). Ergasilus labracis was found to be the most prevalent parasitic copepod sampled from fish in upper Bay d'Espoir (low-salinity and medium-salinity zones: greater than 75%), but rarely on fish from Hermitage Bay/Connaigre Bay (high-salinity zone: less than 15%). Parasite intensities were highest in the low-salinity zone within Bay d'Espoir at 18–22°C, but decreased significantly in Hermitage Bay/Connaigre Bay (salinity > 20 psu; temperature < 18°C. Decreases in parasite prevalence and increases in mean intensity in July and August for low- and medium-salinity zones are likely due to the appearance of smaller young-of-the-year fish hosting fewer parasites, suggesting that during this period larger adults act as the main reservoirs for infection of young-of-the-year fish >3 cm total body length (September). Our data suggest that G. aculeatus could act as a key amplification source for these parasites and thus may impact adjacent aquaculture sites in the bay.