There is an ongoing discussion in Norway to what extent eutrophication symptoms in coastal areas of Norway, such as the disappearance of Laminaria saccharina, are affected by discharges of anthropogenic nutrients or other factors such as higher temperatur e (Moy et al 2008). Preliminary evidence suggests that the non-chlorophyll light attenuation of the Norwegian Coastal Water (NCW) has increased over the last 70-100 years (Moy et al 2008, Aksnes et al. in press) which suggest a general darkening of the wa ter column. This proposal addresses possible effects of such darkening on the eutrophication status of coastal areas. Since the NCW distributes along the entire Norwegian coast, and into all fjords and coastal areas, an elevated non-chlorophyll light atte nuation is likely to be general for all coastal areas although depending on the NCW-thickness. Particularly in the south, where NCW is fresher and more concentrated towards the surface, elevated non-chlorophyll light attenuation might be responsible for c hanges commonly interpreted as eutrophication symptoms caused by discharges of anthropogenic nutrients. This proposal will provide novel knowledge of mechanisms underlying symptoms of eutrophication in general and in particular for Norwegian coastal water s. This in turn will provide knowledge to better clarify the causes of, and thereby the most efficient combat against, observed eutrophication symptoms.