RiverWatch uses the patented Coliscan Easygel method to test for the presence of coliform bacteria. The growth-medium in the bottles contains inhibitors for non-coliform bacteria and pigment colors that identify coliform bacteria.


  1. At the river, use a sterile pipette to add 1 mL of sample water to an Easygel bottle. Label the bottle and keep cool. Dispose of the pipette and wrapper.


  1. Back at school, pour all of the Easygel bottle contents into the sterile and coated Petri dish.
  2. Seal the Petri dish shut with clear tape. Label the dish.
  3. If necessary, gently tip the Petri dish to spread the solution evenly.
  4. Incubate at the warmest room temperature available.

Counting Colonies

  1. After two days of incubation, count the Coliform bacterial colonies:

pink colonies ...

general coliform bacteria that do not necessarily indicate fecal contamination

purple colonies ...

fecal coliforms (E.coli) indicating fecal contamination

white, etc. colonies ...

non-coliform bacteria

  1. Check the colonies against white and black backgrounds to highlight colors.
  2. Counting the total number of pink and purple colonies indicates the number of Coliform bacteria per 1 ml of river water.
  3. Enter your results on-line at . Click on "River Data & Maps" then "Enter Collected Data from your Trip".


  1. Open the Petri dish and add a capful of bleach to kill the bacteria. Reseal, tape, swirl and allow to sit for five minutes.
  2. Dispose in a plastic garbage bag.