Starch-containing plastic films exposed to a natural freshwater environment were shown previously to undergo significant depletion of the starch components. The culture media from a number of starch-hydrolyzing bacteria that had been collected from larvae attached to these films were found to have alpha-amylase activity. Levels of amylase activity increased with culture age. Most of the activity was found to be cell-associated, and correlated on starch zymograms with an activity at about 55 kDa, in the >50% ammonium sulfate fractionation sample. The pH optimum for these amylases was just at or slightly above neutral, with a temperature optimum of about 65 degrees C.