The Blue Lakes is the common name of three karst lakes in the vicinity of Kazan. The natural park includes lakes Bolshoye, Protochnoye and Maloye, as well as the protected natural area around them. The temperature in the lakes is within the limits of 4 – 6 °С both in summer and winter, which is why the lakes are so popular with lovers of cold water training and winter swimming. The recommended alternative for the unprepared people is contemplative recreation and walks along the lakeside. Specifically for that purpose the Maloye Lake has platforms for picnicking designed around it. The crystal clear water that never freezes in winter attracts divers from all over Russia. The Kazan Divers Club is based right there, and they organise diving sessions both during the daytime and at night. The lakes take their name from the remedial blue clay found at their bottom. A short distance away from the lakes is a health resort that treats a variety of diseases. The water in the lakes is so transparent that it creates the optical effect of a lens: the lake seems not more than one meter deep, although in fact it is as deep as 18 m at some spots.