Bacterial genotypes (isolates) were isolated from surface water of 6 lakes and ponds (Cochrane Pond 2, Cochrane Pond 4, Sibbald Lake, Sibbald Meadows Pond, Lower Kananaskis Lake, and Upper Kananaskis Lake) at 3 times (Spring 2009, Fall 2009, and Summer 2011). 2-4 isolates (usually 3) per site-time. Water samples from 2009 were analyzed for concentrations of chlorophyll a, DOC, total dissolved N, total dissolved P, chlorine, sulfate, potassium, sodium, calcium, and magnesium. These data are given on the water chemistry sheet. Some isolates were identified to genus by sequencing 16S rDNA gene. The bacterial IDs sheet gives the genera, with NA indicating isolates that could not be identified because they could not be revived from frozen samples or because DNA extraction and sequencing was unsuccessful. Isolates are coded by the time from which they came (F=Fall 2009, Sp=Spring 2009, Su=Summer 2011), the site from which they came (2=Cochrane Pond 2, 4=Cochrane Pond 4, 5=Sibbald Lake, 7=Sibbald Meadows Pond, 9=Lower Kananaskis Lake, 10=Upper Kananaskis Lake), and then a number distinguishing them from other isolates from the same site and time. So for instance, isolate F10-1 is isolate #1 from Fall 2009 at Upper Kananaskis Lake. Bacterial isolates were reciprocally transplanted into filter-sterilized water from every site-time and their fitness assayed. These data are on the fitnesses sheet. Column headings are as follows. Isolate gives the isolate ID code, as described in the previous paragraph. source.time and source.site respectively give the time and site from which the isolate originated, with site coded as described in the previous paragraph. medium.time and medium.site respectively give the time and site of the water sample in which fitness was assayed. Each assay was replicated twice, as indicated in the Replicate column. Abs gives the change in absorbance of the culture over 24 h as an index of fitness.