The biodiversity of the estuarine complex of seaweeds in Porja Bay of the White Sea was investigated. Hydrobiological surveys of phytobenthic communities were carried out at stations in the intertidal zone to a depth of 1-2 m along sampling lines using collection frames, and at stations in the sublittoral zone to a depth of 2-23 m by scuba-divers in 1980-1990 and 2011. The list of macroalgae in shallow waters of Porja Bay is not so long, with just 49 species, including 7 green, 16 brown and 26 red algae. The species composition is quite peculiar - there prevail annual filamentous algae with considerably dissected thallus, capable of massive development in considerably brackish and low temperature conditions, with extensive fluctuations of salinity and temperature. The (vertical and horizontal) distribution of macroalgae features a complex mosaic following the distribution of hard and soft bottom and brackish water.