This dataset consists of analysed phytoplankton data from the years 2001-2017 inclusive collected in UK waters from the SmartBuoy moorings at Celtic Deep, Dowsing, Gabbard/West Gabbard/WestGabbard2, Warp and Liverpool Bay using WMS and EDU automated water samplers. SmartBuoys consist of a 4 meter tall stainless steel frame with a fibreglass toroid for buoyancy. Instruments are attached at a nominal 1 meter depth to the frame. The water samplers collect into pre-spiked bags containing acidified Lugols Iodine on a pre-determined cycle over the course of a deployment. Following recovery these samples were analysed for a full community of phytoplankton species using the Utermohl method on high-power inverted microscopes. Phytoplankton cell counts are abundance values reported in Cells per Litre.