Lake Kuş or Lake Manyas (Turkish: Kuş Gölü meaning Bird Lake, or, Manyas Gölü) is a lake in western Turkey, located in the Bandırma region. This is a shallow nutrient-rich freshwater lake (average depth 3 m) fed by groundwater and four streams. Small deltas have formed where the latter enter the lake, comprising extensive marshes and tree-lined riverbanks. Narrow belts of reed Phragmites fringe much of the lake. Water is abstracted for factory use and for irrigation. Cattle- and sheep-grazing is common along the lake shores.
Manyas Lake is an important site for breeding and wintering waterbirds. In 1938 the Kuş Cenneti (Turkish for "Bird Paradise") nature reserve was set up by the German zoologist and hydrologist Curt Kosswig who worked in Turkey from 1937-1955. This 64-ha sanctuary occupies a largely unspoiled area of the lakeside near Sığırcık in the northeast corner of the lake and has a small ornithological museum of stuffed birds in poor condition, remote-controlled viewing cameras, and an observation tower erected in 1952 by the Hydrology Department of the University of Istanbul.
High threats include agricultural use and intensification, drainage and dam construction. Artificially high water-levels have resulted in the loss of feeding marshes. Nesting trees in the National Park have also begun to die as a result of prolonged inundation. Agricultural, industrial and household pollution enters the lake in large quantities. Due to over-fishing, disease, pollution and possibly the effects of the changing water regime, fish catches have declined drastically. Fish migration into the lake is now impossible following the construction of a regulator.