The simultaneous behaviour of seven ecological indices(Hurlbert’s, Margalef’s, Menhinick’s, Shannon’s,species number, Jaccard’s and saprobic index) wasstudied based on phytoplankton data close to the shoreon the East coast of Sweden during the summer 1998.The sampling stations had a similar eutrophicationlevel and were located in bays. Standard phytoplanktondatabases were used in calculating the indices, whichwere later compared using cluster analysis.Hurlbert’s, Margalef’s, Menhinick’s, Shannon’s andspecies number indices, as measure of communitydiversity, produced similar trends which oftendiffered from those based on Jaccard’s index ofsimilarity. However, the simultaneous use of theseindices was found meaningful as a possible part of themonitoring close to the shore. The application of asaprobic index lead to erroneous conclusions in thestudied case.