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An iron-poor stream of nearly neutral pH polluted by mine tailings has been investigated for a natural phenomenon responsible for the polishing of heavy metals in mine wastewaters. A white mineralized mat, which was determined to be hydrozincite [Zn5(CO3)2(OH)6] by X-ray diffraction analysis, was observed in the stream sediments mainly in spring. The precipitate shows a total organic matter residue of 10% dry weight and contains high concentrations of Pb, Cd, Ni, Cu, and other metals. Scanning electron microscopy analysis suggests that hydrozincite is mainly of biological origin. Dormant photosynthetic microorganisms have been retrieved from 1-year-old dry hydrozincite. The autofluorescent microorganisms were imaged by a scanning confocal laser microscope. A photosynthetic filamentous bacterium, classified as Scytonema sp. strain ING-1, was found associated with microalga Chlorella sp. strain SA1. This microbial community is responsible for the natural polishing of heavy metals in the water stream by coprecipitation with hydrozincite. Abandoned mines present a high environmental hazard in all countries today. In several parts of the world where mining activities have shut down, the problem of the control and reclamation of polluted areas for new activities arises. The polishing of metals from a mining area is a difficult task. The transformation of metals into harmless species or their removal in a suitable recycled mineral form such as carbonates (1, 15) is a possible solution for the remediation of a mining area. Therefore, research in this field continues, with the isolation of new strains with more-successful mechanisms for the reduction of metal toxicity. At Ingurtosu (southwestern Sardinia, Italy) lead and zinc sulfide ore deposits were mined until 1968 and tailings were deposited along the Rio Naracauli creek. The MontevecchioIngurtosu deposit consists of galena-sphalerite veins in a quartz gangue containing iron, calcium, and magnesium carbonate minerals. Pyrite, chalcopyrite, barite, cerussite, and anglesite are the most commonly associated minerals (22). Previous studies in this area have shown that waters are highly polluted by heavy metals, in spite of their near-neutral pH (4‐6, 30).