Before the 1980s, the bladderwrack (Fucus vesiculosus) formed extensive belts along the SW coast of Finland, but already then it began to decline especially in sheltered bays of the inner archipelago. We studied underwater vegetation by scuba diving in 1993–2007. By 2007, six out of eleven sites had lost their Fucus belts, and sheltered bays had become refuges for the bladderwrack. In 2006–2007, we studied the effects of temperature, transparency, bottom type, shoreline orientation and location on the bladderwrack distributions and depth penetrations at 61 locations across different archipelago zones. Of these, only location indicated a possible effect.