Paleoclimate studies of continental environments have been hampered by the lack of an independent paleotemperature proxy. A novel sea-surface temperature proxy has been proposed for marine systems based on membrane lipids of marine crenarchaeota (the TEX86—tetraether index of tetraethers with 86 carbon atoms). Analysis of archaeal membrane lipids in core-top sediments from a diverse suite of lacustrine systems suggests the ubiquitous occurrence of low-temperature crenarchaeota in lake systems as well. Application of the TEX86 proxy in these lacustrine systems indicates that it is valid in lake environments, and the calibration of TEX86 in lacustrine systems is similar to that in the marine environment. This proxy will provide an independent continental paleotemperature tool that will allow paleoclimatologists to address fundamental questions about temperature variability in continental environments and its relationship to climate change.