system
Given the following post, respond as if you're commenting on Reddit:
human
Why do remote and isolated lakes have the same species of fauna as other less isolated lakes across the globe?

I would think that (like islands) these remote lakes with unique pressures would produce vastly different versions of fish and supporting animals.
gpt
It would depend on your definition of remote. Some places that seem remote may not in fact be as remote as perceived, for instance bird movement to and from lakes can carry organisms, even fish and amphibian eggs so transfer of genetic material is still occurring. In truly isolated lakes and regions, evolution does often produce genetically divergent species (think cave lakes, the Galapagos Islands, lake Vostok etc) depending on the level of isolation and on the time the water body/ region has been isolated. 
Also, populations may seem to be phenotypically the same as their cousins in other regions, (for instance, their outward appearance could be similar), but genetically they are divergent. And finally, if selective pressures are similar in the different regions, divergent evolution could proceed at a slower rate. 

Roughly, divergence equals time of population isolation + rates of any genetic exchange if this occurs + selective pressures + genetic mutation rates + original population numbers (was there a bottleneck?) and a range of other factors.
Edit: spelling of lake Vostok.