Phytoplankton communities in the crater lakes of western Uganda, and their indicator species in relation to lake trophic status

•Ugandan crater lakes cover wide gradients of aquatic productivity and human impact.•Most lakes are dominated by cyanobacteria, including those that are least productive.•Phytoplankton communities can be clustered in four groups linked to trophic level.•Their chl-a boundaries are higher than those between traditional trophic categories.•Each cluster contains one or more primary and/or accessory indicator species.