The Heavy metal contamination is an issue of global concern. It is a major environmental problem posed by the mining industry worldwide, affecting most countries. Porgera mines discharge waste (tailings and soft rocks) into the Lagaip/Strickland River system, thus rendering the river system at risk of heavy metal contamination. Sediment samples were collected along selected sites of the river systems and analyzed for specific metals i.e., Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn using ICP-MS. The contamination level of heavy metals in sediments was evaluated using pollution indices, including contamination factor, degree of contamination, modified degree of contamination, and Nemerow's pollution index. Ecological risk assessment was performed using ecological risk factors, potential ecological risk indices, and consensus-based sediment quality guidelines. The results indicate that Pb, Zn, and Cd pose long-term risks in the Lagaip Strickland reservoir, whereas the rest of the heavy metals were regarded as less hazardous based on sediment quality assessments.