Assessing the impact of urban catchment runoff on receiving waters must be addressed. Trace metal contamination represents a significant risk to the environment and public health. But total concentration does not reflect trace metal environmental impact because their toxicity depends especially on the nature of present species. Most studies address the fate of trace metals in lake tributaries or in lake sediments. Our aim was to focus on the seasonal variation of trace metal concentrations in the lake water column in order to improve the assessment of urban runoff impact. This study focuses on the seasonal monitoring, for 10 months including dry and raining seasons, of trace metal concentrations and their speciation in the water column of Lake Pampulha. Trace metals were collected at two depths in the middle of Lake Pampulha. For each collected sample, metal fractions were divided into total, dissolved, and inert metal. Six anthropogenic trace metals were considered: cadmium, cobalt, copper, lead, nickel and zinc. The results showed different behaviour of trace metals in the water column. Cadmium concentration is under the quantification limit. Speciation results indicate a variable metal bioavailability. Zinc is the most bioavailable (~60%). Bioavailability of cobalt which is highly dissolved varies with depth. Nickel bioavailability remains rather constant in the surface layer during the study period and those of copper, zinc and lead are more variable.