Western Mongolia contains a variety of lakes ranging from freshwater to more saline than the ocean.  Their diversity and isolation provides an opportunity to examine regional biodiversity of an aquatic invertebrate fauna across extreme chemical and spatial scales. Ten lakes with specific conductance ranging from 41-8610 µS were sampled for chironomid surface floating pupal exuviae in August 2004.  Although a total of 58 chironomid taxa were collected, richness by lake was low, ranging from 4 to 22 and averaging only 12 taxa per lake.  Richness was lower in lakes with conductivity of 473 µS or higher, with a mean of 8 taxa compared to 16 taxa in lakes with conductivity <473 µS.  Similarity in taxa composition among lakes also was low, with an average Sorenson Similarity Index value of 0.20.  Most taxa were not widely distributed, with 41% of taxa collected in only one lake and 90% in three or fewer lakes.  Only six taxa were emerging from more than three lakes.  A total of 166 chironomid species are known from Mongolia.  Consequently, the equivalent of more than a third of the taxa known from this country emerged in August from ten lakes suggesting these habitats are relatively diverse.