Radon Springs in Lopukhinka, Natural monument in Leningrad Oblast, Russia

Radon Springs in Lopukhinka is a 270-hectare geological and hydrological nature monument in the Lomonosov District, formed in 1976. Springs emerging from the Cambrian-Ordovician aquifer feed the Lopukhinka River and have cut a canyon up to 30 metres deep. Two dams in the upper canyon hold back elongated artificial lakes about 50 metres wide and 200 and 500 metres long, with a fish nursery, Ruditsa, below the lower dam.

The site became a protected natural monument on 29 March 1976, when the Leningrad Oblast executive committee set aside about 270 hectares between the villages of Lopukhinka and Verkhniye Ruditsy. Two small dams were built in the upper canyon to regulate the springs and the Lopukhinka River, creating two elongated ponds about 50 metres apart, 50 metres wide and 200 and 500 metres long. A fish nursery, Ruditsa, lies below the lower dam.

The undergrowth includes lungwort, hepatica, spring vetch, and the rare broad-leaved bellflower. The reserve permits only sanitary felling, mushroom and berry picking, and educational excursions for students. The Lopukhinka River, a tributary of the Kovasha, holds protected brown trout.

The reserve covers 270 hectares in the south of Lomonosovsky District, between the villages of Lopukhinka and Verkhniye Ruditsy. An ecological trail circles the upper lake and begins at a small bathing area. Reach it from St Petersburg via Petergof, then a bus toward Koporye to the Lopukhinka stop. Building, industry and anything that pollutes the site are prohibited.

The springs rise from the Cambrian-Ordovician aquifer, whose water carries a high concentration of radioactive elements, radon above all. The radon comes from deeply buried shales, not from limestone or sandstone. Two small dams in the upper canyon hold back the flow, forming lakes 200 and 500 metres long, about 50 metres apart.