Community interactions can be altered by numerous external forces, including anthropogenic chemical stressors. Such stressors have become more important with increased human pressure on water resources. Room-temperature ionic liquids (ILs), an emerging class of industrial solvents with many potential applications, are likely to contaminate aquatic ecosystems via wastewater and accidental spills. However, little understanding exists of potential population or community-level impacts of ILs. We studied IL effects on the benthic consumer Dreissena polymorpha (zebra mussel), the pelagic consumer Daphnia magna (waterflea), and a common food source, the phytoplanktor Chlamydomonas reinhardtii. The ionic liquid 1-butyl-3-methylimidazolium bromide was highly toxic to all these organisms (LC50_Dreissena = 1290.6 ppm; LC50_Daphnia = 8.13 ppm; EC50_{Chlamydomonas} = 1071.0 ppm), altering rates of survivorship, reproduction, and consumer feeding. Experimental results were used to parameterize mathematical models from which we made predictions about IL effects on community dynamics. These models showed that ILs dramatically altered community dynamics, primarily by eliminating Daphnia and releasing Chlamydomonas from herbivore pressure; Dreissena were largely unaffected. Combining experimental results with mathematical models provides a more complete picture of the potential effects of novel chemicals, such as ILs, on aquatic ecosystems.