The main limnological features of Lake Issyk-kul are described. The lake is a large (6,236 km2), deep (zm, 668 m), closed lake in eastern Kirgizia. It lies at ∼1,607 m above sea level, but water-levels have been dropping since the last century. It is slightly saline (salinity, ∼6g L−1), with Na+, Mg2+, Cl− and SO 4 2− the dominant ions. Nutrient levels are low and the lake is considered ultra-oligotrophic. Characeae dominate the macrophytes. About 300 and 117 taxa of, respectively, phytoplankton and zooplankton have been identified, withArctodiaptomus salinus the most numerous in the zooplankton. Chironomids dominate the benthos. Several endemic taxa of fish occur, of whichLeuciscus bergi was dominant until the 1970s. The fish fauna has been supplemented by many introduced species. Three mysids were introduced in 1965–8 and are now a significant part of the ecosystem. The present annual fish catch permitted is 320 t. The most important value of the lake is as a recreational resource. To promote and sustain this value requires careful, ongoing management. The most significant threats to the lake are local pollution, visitor pressure, and declining water-levels.