Elevated levels of pollutants, including heavy metals, resulting from human activities, have raised concerns regarding their adverse impacts on natural ecosystems. Among these, aquatic organisms, particularly non-target microalgae, bear substantial consequences from such contaminants. This study endeavored to evaluate the impact of the heavy metal lead (Pb) at concentrations of 2.5, 25, and 250 μg L⁻¹ on the growth and lipid content of the diatom Cyclotella meneghiniana in a 14-day toxicity test conducted under controlled laboratory conditions. The findings indicate that lower Pb concentrations (2.5 and 25 μg L⁻¹ ) fostered algal proliferation, whereas exposure to 250 μg L⁻¹ resulted in complete inhibition in two distinct endpoints. Additionally, no significant fluctuations in algal lipid content were discernible between exposure to 2.5 and 25 μg Pb L⁻¹ and the control group. This study stands as a pioneering effort in unveiling the toxicity of Pb on C. meneghiniana, shedding light on the species’ susceptibility to this heavy metal and underscoring the necessity of incorporating this species into ongoing ecological risk assessments of Pb.