As assigned by the Provincial Government of Åland Islands, a mapping of underwater vegetation was carried out by using SCUBA in the archipelago of Åland Islands. The mapping was done along two inner–outer archipelago gradients in the Northwestern and Southeastern coastal areas. The purpose of the mapping was to follow up possible changes in the macrophyte assemblages since 2004, when the mapping on these sites first was carried out. In this study, two new localities were also visited in the Southeastern archipelago. The macrophyte assemblages were investigated qualitatively and quantitatively along a 50 m long transect. The limits of vertical distribution of the macrophytes were noted along with several environmental parameters that can affect the macrophyte assemblages. A total of 42 species of macroalgae and plants were encountered. The most important factors affecting the composition of the macrophyte assemblages and the number of species was the bottom type and water quality. The sites along the Northwestern gradient had not changed significantly according to the composition of the assemblage or number of species since 2004. The water transparency had decreased since 2004 along both gradients except in the inner and middle archipelago zones in the Southeastern coastal area. This could be seen as a decrease in the vertical distribution limits of the macrophytes. The Northwestern gradient was still less affected by anthropogenic disturbance had lower nutrient levels and better water transparency than the Southeastern gradient. Bladderwrack (Fucus vesiculosus) had disappeared from several outer archipelago sites along the Southeastern gradient, which can be seen as a sign of continuing eutrophication in this area
