> Abstract The dominant members of the bacterioplankton community in a set of 10 small, thermally stratified lakes in northeastern Indiana were determined by denaturing gradient gel electrophoresis (DGGE) of a polymerase chain reaction amplified fragment of 16S rDNA. The variability in community composition was analyzed as function of vertical stratification (epilimnion vs metalimnion), time (July vs August samples), and geographical location. In 58 discrete samples, a range of 8-23 bands were detected (mean = 14, s.d. = 4). For all variables, sample pairs shared about 40-70% of bands. In comparisons between depth strata, pairs of oxic samples shared more bands than an oxic-anoxic pair. There was no obvious relationship between the geographical location of lakes (or their physical connection) and band sharing.http://link.springer-ny.com/link/service/journals/00248/bibs/38n2p126.html