Tjärven lighthouse, Maritime lighthouse in Norrtälje Municipality, Sweden

Tjärven is a lighthouse built in 1902–1903 on a small, exposed skerry surrounded by deep water, 2 nautical miles north-northwest of Söderarm. Its original national-romantic design resembled a medieval castle, with crenellations on the roof and bay windows. A 1952 renovation gave it a functionalist look, cladding the facade in eternit panels and replacing the lantern.

A day beacon stood on Tjärven by the mid-19th century, documented in 1872 and fitted with a pole marker in 1882. The Åbo maritime association proposed a lighthouse in 1892, but only a royal decision of 28 April 1902 authorised construction. Building began in May 1902 and the light was first lit on 1 November 1903.

The island's name appears as Kerven on Anders Bure's 1626 map and as Kjärfven on an 1805 survey chart, which also shows the now-dry harbour inlet Tjärvarhamn on its east side. John Ajvide Lindqvist set his 2011 short novel "Tjärven" here, a midsummer class reunion overrun by zombies.

The island can be reached by boat in acceptable weather, but docking is difficult on this remote, slippery skerry. Cruise ships between Sweden and Finland pass close by, and anchoring or diving east of the light is dangerous because of possible World War I Russian mines on the seabed.

The waters surrounding the lighthouse contain unexploded Russian mines from World War I. This historical hazard makes diving and anchoring near the site extremely dangerous and represents a hidden legacy of the war in these waters.