During the 1990s, there was a rapid expansion of salmon farming in Norway, with observations of escaped farmed salmon in many rivers, and reports of high salmon louse infections in anadromous brown trout. National authorities became increasingly concerned about the potential detrimental impacts of salmon aquaculture on wild populations; there was a growing awareness of the need for greater genetic and ecological knowledge about wild populations and the interaction between aquaculture wild salmonids. A decision was made to use the river Guddalselva, located in the Hardangerfjord, as a “river laboratory”- i.e. as an experimental facility to study the interaction between aquaculture and wild salmonid populations in 2000 as a joint effort between several management authorities, river owners and research institutions.