Samples were collected as part of a FRST-funded freshwater biodiversity programme, between 1998 and 2004. Samples were collected from a range of freshwater habitats throughout New Zealand. Diatom species were listed from permanent slide mounts of diatom frustules (extracted from each sample by removing organic material using strong oxidisers). In most cases, the relative abundance of each species was noted using a scale of 1 (rare) to 5 (dominant). The slide collection is held at NIWA, with slides referenced by the sample number. Photographs of each specimen identified are held on NIWA's Atlas database.