Frednes Bridge is a double-leaf bascule bridge on Highway 356 in Porsgrunn Municipality in Telemark county, Norway. The 461.5 m long bridge crosses the Porsgrunn River (Porsgrunnselva) just before it flows out into the Frierfjord at the site of Norsk Hydro's factory complex on Herøya. The bridge was completed in 1995. It is constructed of prestressed concrete with a steel drawbridge span over the main channel. It is 461 m long, with a main span of 60 m, and beneath it, there is a clearance for vessels of 13 m at mean water level. Frednes was the historic name of an old district of the town of Porsgrunn as well as the name of the Frednes farm. Frednes was purchased by shipping magnate Christen Knudsen who moved there with his family in 1855. The manor house was expanded in 1865, but burned down in 1952 and was not rebuilt.