South Atlantic Water Science Center

Due to a lapse in appropriations, sampling for Bacterialert has been temporarily discontinued. Additionally, USGS will not be able to respond to inquiries until appropriations are enacted. For more information, please see

Chattahoochee River BacteriAlert: Water-sample analysis

The bacteria analysis for total coliform and E. coli is an enzyme substrate method called Colilert that is analogous to the commonly used multiple tube method. Bacteria counts are expressed as a most probable number (MPN) per 100 milliliters (mL). Three or four different dilutions are prepared for each site by adding an aliquot of sample to sterile, deionized/distilled (DI) water to produce 100 mL of liquid. A powdered reagent is added to each dilution bottle and the mixture added to a sterile, plastic tray containing 97 wells and incubated for 20 hours at 35 degrees Celsius. The wells produce a yellow color when total coliform bacteria are present and fluoresce under UV light when E. coli are present.

Graphic showing the water sample analysis process.
Picture showing plastic tray with some cells indicating that total coliform is present (cells are yellow, rather than clear). Picture showing plastic tray with some cells indicating that E.coli coliform is present (cells glow a blue color).