Lilla Värtan or simply Värtan is a strait in Stockholm, Sweden. Separating mainland Stockholm from the island and municipality Lidingö, it stretches from Blockhusudden in the south to Stora Värtan in the north. Two bridges, collectively called Lidingöbron stretch over the strait.While most of the coasts surrounding the strait are occupied by industries and the ferry terminals and oil tanks in the harbour area of Värtahamnen, natural beaches are found in both the southern and the northern end of the strait and the strait forms part of the Royal National City Park.Most common fish species are Baltic herring, sea trout, and salmon. Stationary predator fishes, e.g. northern pike and perch, are exposed to raised levels of mercury.The area is considered an important wintering location for several birds species, including swans, Eurasian coot, common pochard, tufted duck, black-headed gull, lesser black-backed gull, gadwall, and common tern. The strait constitutes an important locale, especially ice-free winters, besides the lake Isbladskärret on Djurgården.