The purpose of our study was to investigate the sub-lethal effects ofmillimeter wave carbon fibers (MWCF), a military obscurant, on filter-feeding freshwater invertebrates. We observed decreased survival, reproduction, and oxygen consumption in Daphnia magna realistic loading rates. In experiments with theAsiatic clam(Corbicula fluminea), soft tissue dry weight and tissue condition index were not significantly different among control and MwcF exposed treatments, however, using a 15N labeled alga asfood, we observed decreased nitrogen turnover in tissues of clams exposed to MWCF,suggesting lower filtering or ingestion rates. Our findings combined withprevious demonstrations of MWCF toxicity to green algae suggest that over a period of several months, bivaMe growth may be inhibited, and cladoceran populations may be even more strongly affected by MWCF Given that these fibers are persistent, furtherexperiments should be conducted to determine the longer-term effe of contamination of waterbodies withMwcF