Samples were collected in a visiting scientist project (W. Vyverman, K. Saabe; University of Ghent, Belgium), within the FRST-funded freshwater biodiversity programme, in early 2001. All samples were benthic grab samples (composites of several subsamples). A comprehensive suite of environmental data (including water chemistry) was collected at the same time. Identifications were done at the University of Ghent, to genus level except for some probably endemic taxa. Voucher slides of each sample are held in the NIWA diatom collection (slide numbers are the same as the siteID).