Lake Yenicaga is situated on the migration route of birds crossing through the Straits. The area around the lake is an important peat deposit and a wide variety of vegetation types and bird species are found in its basin. Although it is an ecosystem that has the potential to become a candidate site for Ramsar designation, conservation status has not yet been assessed. In recent years, immense pressure due to pollution in Lake Yenicaga has brought eutrophication problem. Within the scope of this study conducted monthly between March 2008 and February 2009 on Lake Yenicaga, the variations in water quality and in trophic status were evaluated by comparing the data obtained during the previous studies. The study included several water quality parameters (K+, Na+, Mg+2, Ca+2, Cl, SO4-2, HCO3-, CO3-2, NO3, NO2, NH4, PO4) and chlorophyll a in three sampling stations.