Outbreaks of diseases in recreational waters are frequent and cause death worldwide. The EPA established the water quality standard for the fecal indicator bacteria (FIB), Escherichia coli, to determine when there is a risk to public health in the U.S. However, a quick method to detect and quantify E. coli in situ is needed. In this work, we developed a paper-based device for pathogen detection with a focus on FIB E. coli. T4 bacteriophages were physically adsorbed on paper and able to capture E. coli in 5 minutes. For the first time, metabolic changes of bacteria in lake water were considered for designing two colorimetric assays for detection. The limit of detection (LOD) was 104 colony forming units (CFU) (p<0.05) and the color could be observed by the naked eye on the paper within an hour at room temperature. A pre-concentration was coupled to this technology achieving a LOD 5 X 105 CFU in 100 milliliters filtered. The conditions of assays are field-friendly for testing even in remote places and developing countries.