Lake Peipsi and Lake Võrtsjärv are large shallow lakes which are situated in Northern Europe and are part of the Baltic Sea basin. The two lakes are connected by the Emajögi river which drains from Lake Võrtsjärv to Lake Peipsi.

Lake Peipsi is the largest transboundary water body in Europe and the fourth largest lake in Europe. The area of Lake Peipsi is 3,555 sq. km [km²], of which 44 % belongs to the Republic of Estonia and 56 % to the Russian Federation. Peipsi is a shallow lake; its average depth is 7.1 m and maximum depth 15.3 m. Up to one million migratory birds like geese, swans and ducks use Lake Peipsi as a resting place every year. 100 couples of White Stork and 30 - 40 couples of Corn-crakes are breeding there.

Lake Peipsi is a eutrophic and biologically highly productive lake. The major threat to water quality in the lake is eutrophication, which is caused by the high nutrient load. Agriculture is the main source of nutrient water pollution and the oil-shale industry has big influence to the outlet from Lake Peipsi – the Narva River. One part of this pollution is coming through Rannapungerja River directly into Lake Peipsi.

The lake is most important as a resource for fisheries and recreation. Peipsi is one of the best lakes in Europe for commercial fishing, with a total catch of 8,000 - 11,000 tons/year. The fish stock in Lake Peipsi is one of the richest in Europe. Besides eutrophication unregulated fishing in the lake is one of the most critical environmental issues for the Peipsi watershed.