Data Accessibility Statement
Raw sequence reads have been deposited in the European Nucleotide Archive (ENA) at EMBL-EBI under accession number XXXXXX (https://www.ebi.ac.uk/ena/browser/view/XXXXXX), and associated sample metadata are archived in the Dryad repository (DOI). The microscopy-based monitoring record of phytoplankton genus occurrence from 1945 to 2010 is available in Supplementary Information B. The physicochemical record from Esthwaite Water is available at: https://doi.org/10.5285/87360d1a-85d9-4a4e-b9ac-e315977a52d3 (Maberly et al ., 2017).