We investigated if in-situ metal bioprecipitation (ISMP) is applicable to remediate a highly permeable zinc-contaminated aquifer at a metal-processing factory in Maasmechelen, Belgium. A large (more than 200 m long and 70 m wide) groundwater contamination plume has developed, with zinc concentrations in the range of 1 - 100 mg/L, whereas the legal Flemish clean-up standard is 0.5 mg/L.