Chlorophyll a is ubiquitous in phytoplankton and higher plants and a proxy for phytoplankton biomass. It is a pigment held within light harvesting complexes associated with photosystems driving photosynthesis and the units for chlorophyll are μg/L. Cyanobacteria are also considered as phytoplankton as then contain chlorophyll a but they are not algae. Hence, measures of chlorophyll a should recognise and account for the contributions from cyanobacteria.