Two out of three datasets (the first one already published with Hugerth et al 2015) included in the Baltic Sea reference metagenome assembly. The assembly include herein is a coassembly of all three datasets, complete with annotated genes to facilitate further studies of the Baltic Sea with much less computational effort. The assembly is constructed using 2.6 billion metagenomic reads from 81 water samples, spanning both spatial and temporal dimensions, and contains 6.8 million genes that have been annotated for function and taxonomy. The assembly is useful as a reference, facilitating taxonomic and functional annotation of additional samples by simply mapping their reads against the assembly.