Chistoe Lake, Protected natural area in Tatarstan, Russia.

Chistoe Lake (Tatar: Chista Kül) is a closed karst lake 2.7 km east of the village of Chistoe Ozero in the Laishevsky district of Tatarstan. It has a complex outline, 820 m long and up to 220 m wide, with a surface of 7.8 hectares, an average depth of 4 m and a maximum of 14 m. Its bluish, odourless water is of the hydrocarbonate-calcium type, with a hardness below 1 mmol/l and a transparency of 90 cm.

Chistoe Lake was designated a natural monument of regional significance by a resolution of the Council of Ministers of the Tatar ASSR on 10 January 1978 (No. 25). A second resolution of the Cabinet of Ministers of the Republic of Tatarstan, No. 644 of 29 December 2005, confirmed this protected status. The lake lies 2.7 km east of the village of Chistoe Ozero in the Laishevsky district.

The lake's Tatar name, Chista Kül, and the Russian Chistoe both mean 'clear', and the village 2.7 km to the west is called Chistoe Ozero after it. The water is still described as bluish and odourless, with a transparency of 90 cm, so the name matches what a visitor can see. The lake supplies household needs, bathing and watering of garden plots.

The lake lies 2.7 km east of the village of Chistoye Ozero in the Laishevsky district; the water is fed by underground sources and stays stable. The shoreline is reached over open terrain, and the water is used by locals for swimming and watering garden plots. Self-purification of the lake is weakened, so keep the banks clean.

The lake has no surface outlet: it is a karst basin fed by groundwater, and its self-purification is described as weakened. Its water is hydrocarbonate-calcium, with hardness under 1 mmol/L and mineralisation of 51.1 mg/L. Local residents use it for household needs, bathing and watering garden plots.