The determination of phytoplankton chlorophyll is held with the method of Golterman (1978). The method is based on the property of chlorophyll to absorb light in the red zone of the visible spectrum. From the sample concentrated on Watman GF/C da 0,45 μ filters, after homogenization, the chlorophyll is extracted with 90% acetone for 24 hours, in the dark and under refrigerated conditions. Subsequently, the samples are centrifuged at 3000 rpm for 30 minutes and the concentration is determined by reading the UV-visible spectrophotometer at the wavelengths of 665 and 750 nm. In the presence of degradation products, the emission of which interferes with that of chlorophyll a, the estimation of the pigments can be carried out more correctly through the acidification of the extract with 0.1M HCl. At acid pH, chlorophyll a loses the magnesium atom from the porphyrin nucleus and converts with a stoichiometric ratio into phaeophytin a. The use of appropriate equations subsequently allows to algebraically calculate the concentrations in the sample of both chlorophyll a and the sum of the degradation products (pheopigments).