This project examines the effect of acid mine runoff on meioflora/meiofauna community structure in a mineshaft outflow pool. Water chemistry tests and biological sampling were performed during fall/winter of 2004 at a mineshaft pool, an acid-impacted stream and a reference stream receiving no acid runoff. The mineshaft pool had the highest levels of pollutant species (iron, copper, sulfate, etc.) and the lowest pH (2.5). The dominant organisms were two species of algae, Chlorhormidium sp. and Eunotia sp.; other species included two rotifers, a tardigrade, a nematode, and various ciliates (especially Stylonychia). Five species of diatoms and flagellates were found in the acid-impacted stream, which had high pollutant levels and a pH of 3.5. The reference stream, which had low pollutant levels and a pH of 6.5, contained diatoms, ciliates, a rotifer, a flagellate, and desmid algae. The results indicate that the diversity of acid-impacted ecosystems is higher than expected.