A description of biological and ecological data of the Danube delta lakes and channels is presented. The biological indicators refer to aquatic macrophytes, fish, zoo-plankton, and macro-invertebrates. Environmental data include physio-chemical data as well as hydrological parameters. More information on this dataset can be found in the Freshwater Metadatabase - MARS_12 (http://www.freshwatermetadata.eu/metadb/bf_mdb_view.php?entryID=MARS_12