Treated wastewaters in the United States contain detectable quantities of surfactants, antibiotics, and other types of antimicrobial chemicals contained in pharmaceutical and personal-care products (PPCPs) that are released into stream ecosystems. The degradation characteristics of many of these chemicals are not yet known, nor are the chemical properties of their byproducts. They also are not currently mandated for removal under the U.S. Clean Water Act. Three representative PPCPs were individually tested in this study using a series of laboratory dilution bioassays: Ciprofloxacin (an antibiotic), Triclosan (an antimicrobial agent), and Tergitol NP 10 (a surfactant), to determine their effects on natural algal communities sampled both upstream and downstream of the Olathe, KS wastewater treatment plant (WWTP). There were no significant treatment effects on algal community growth rates during the exponential phase of growth, but significant differences were observed in the final biomass yields (p < 0.001). All three compounds caused marked shifts in the community structure of suspended and attached algae at both the upstream and downstream sites (p < 0.05). Increasing the concentrations of all three compounds over a 3 orders of magnitude range also caused a consistent decline in final algal genus richness in the bioassays. Our results suggest that these three PPCPs may potentially influence both the structure and the function of algal communities in stream ecosystems receiving WWTP effluents. These changes could result in shifts in both the nutrient processing capacity and the natural food web structure of these streams.