The rare earth element (REE) concentrations of lake water from five alkaline lakes (i.e., Mono, Walker, Abert, Summer, and Goose Lakes) within the Great Basin of the western U.S.A. are reported. All of the lakes exhibit HREE-enriched shale-normalized patterns. The speciation of the REEs was determined and, in all cases, species greater than 99% of each of the REEs exist as Ln(CO3)2 complexes. The only exception to this is Summer Lake where minor amounts of phosphate species were also predicted. The large enrichments in the HREEs observed in these lakes are the result of the formation of stable carbonate complexes in solution where the HREEs preferentially form stronger carbonate complexes than the LREEs. Activity product calculations for REE phosphate coprecipitates in these lakes indicate the lakes are close to saturation with respect to these phases and suggest that these precipitates may limit the maximum dissolved REE concentrations in the lakes. ¿American Geophysical Union 1994