Ten production wells drilled in a highly productive sand and gravel aquifer, recharged by an adjacent river, were evaluated for potential Giardia and Cryptosporidium contamination. The goal of this study was two-fold: to determine if a correlation exists between the occurrence of surface water indicators and Giardia and Cryptosporidium; and, to examine riverbank filtration as a microbial treatment process. Pathogen monitoring was conducted sporadically over ten years. Intensive monitoring was conducted for a twenty-month period at ten "flowpath wells" and two production wells. Algae, diatoms and other surface water indicators were found in 57% of 128 groundwater samples. Of 285 groundwater samples collected and analyzed for Giardia or Cryptosporidium, no pathogens were detected. No correlation existed between Giardia, Cryptosporidium and surface water indicators. All surrogates demonstrated a minimum 4-log reduction. Even though there is hydrologic influence, riverbank filtration is highly effective in removing pathogenic protozoa. Includes 26 references, tables, figures.