Type genome is Fontibacterium temperatum ZE-03apr19-LR-3 (GCA_964203055.1), a metagenome-assembled genome (MAG) assembled from 5 m depth from Lake Zurich, Switzerland (date: 2019-04-03). ZE-03apr19-LR-3 has a genome size of 0.9 Mbp with a genomic GC content of 29.4% and contains 28 tRNAs. The genome is of high quality, consisting of 3 contigs, with a completeness of 94%, contamination of 0% and strain heterogeneity of 0% as assessed with checkM. The metagenome was assembled with FLYE from combined long-and short-read sequencing (Oxford Nanopore and Illumina NovaSeq). Metagenomic fragment recruitment of >600 samples from five continents indicate that the species is highly abundant in temperate lakes of the Northern Hemisphere. The closest cultivated relatives are Fontibacterium commune, syn. ‘Candidatus Fonsibacter ubiquis’ LSUCC0530 (GCF_002688585.1; later reclassified to ‘Ca. Allofontibacter communis’), with an average amino acid identity of 87.44% and average nucleotide identity of 85.23% and another newly proposed species, Fontibacterium abundans MiE-29 (GCA_965235095.1), with an AAI of 93.82% and an ANI of 92.5%. Current GTDB classification (R220): d__Bacteria; p__Pseudomonadota; c__Alphaproteobacteria; o__Pelagibacterales; f__Pelagibacteraceae; g__Fonsibacter; s__Fonsibacter sp000510845.