Mining activities often are associated with metal contamination of the nearby terrestrial and aquatic environments. Hence, the present study was performed in a section of the river Thigithe flowing beside North Mara Gold Mine (NMGM) (Nyamongo Area) in Tarime district, Tanzania. The aim was to assess the effect of gold mining activities on the metals distribution in the aquatic ecosystem of river Thigithe. Surface water, sediment and tissues (muscles, gills, livers) of the most common and abundant fish (Labeo victorianus) were sampled during the dry season (August 2013). In these samples, the following trace elements were analysed: Cd, Pb, Cr, Co, Ni, Cu, Zn, As and Hg. Results show that concentrations of all metals analysed in the surface water were below or near the detection limit. Regarding the sediments, the average concentrations of metals were higher in sites upstream of the mine compared to more downstream sampling sites. Very high concentrations of arsenic were recovered, ranging from 17.14 - 31.59 µg/g dw. However, for the other elements, concentrations of all metals fell below or slightly above the crustal background concentrations. In addition, when compared to sediment quality guidelines, sediments were not toxic for aquatic benthic fauna. These findings show that the mineralogy of the area is the potential source of metals for the sediments. In general, concentrations of metals in fish gills and liver tissues were relatively higher than in muscle samples. Metal concentrations in fish tissues were comparable to slightly higher compared to metal levels in tissues of fishes from unpolluted environment in other regions. The health risk by consuming contaminated fish was assessed. Compared to FAO/WHO (1995) and European community (2006) maximum levels of contaminants in foods, the measured metal burdens in fish muscles do not pose health risks to humans upon fish consumption. Based on the Minimum Risk levels (MRLs) of a contaminant that an average 70kg person can take per day through oral route without suffering health risks, As had the lowest edible amount of fish muscle and Ni the highest.