A method for monitoring and controlling hydrophobic contaminants in an aqueous stream of a pulp or papermaking process, the method comprising conducting a sample of the aqueous stream to an optical measurement device, the sample containing solid particles; adding hydrophobic dye to the sample, fractionating the sample into one or more fractions according to particle size and/or particle mass, measuring fluorescence intensity values and light scattering intensity values for each of the one or more fractions, wherein the method further comprises: - adding together the fluorescence intensity values of the fractions thus obtaining a sum of the fluorescence intensity values, - adding together the light scattering intensity values of the fractions thus obtaining a sum of the light scattering intensity values, - calculating a hydrophobicity density of the particles in the sample by dividing the sum of the fluorescence intensity values with the sum of the light scattering intensity values, and - monitoring and controlling the concentration of hydrophobic contaminants in the aqueous stream based on the calculated hydrophobicity density of the particles in the sample, or - adding together the fluorescence intensity values of a fraction thus obtaining a sum of the fluorescence intensity values in the fraction, - adding together the light scattering intensity values of the fraction thus obtaining a sum of the light scattering intensity values in the fraction, - calculating a hydrophobicity density of the particles in the fraction by dividing the sum of fluorescence intensity values of the fraction with the sum of light scattering intensity values of the fraction, and - monitoring and controlling the concentration of hydrophobic contaminants in the aqueous stream based on the calculated hydrophobicity density of the particles in the fraction. conducting a sample of the aqueous stream to an optical measurement device, the sample containing solid particles; adding hydrophobic dye to the sample, fractionating the sample into one or more fractions according to particle size and/or particle mass, measuring fluorescence intensity values and light scattering intensity values for each of the one or more fractions, wherein the method further comprises: - adding together the fluorescence intensity values of the fractions thus obtaining a sum of the fluorescence intensity values, - adding together the light scattering intensity values of the fractions thus obtaining a sum of the light scattering intensity values, - calculating a hydrophobicity density of the particles in the sample by dividing the sum of the fluorescence intensity values with the sum of the light scattering intensity values, and - monitoring and controlling the concentration of hydrophobic contaminants in the aqueous stream based on the calculated hydrophobicity density of the particles in the sample, or - adding together the fluorescence intensity values of a fraction thus obtaining a sum of the fluorescence intensity values in the fraction, - adding together the light scattering intensity values of the fraction thus obtaining a sum of the light scattering intensity values in the fraction, - calculating a hydrophobicity density of the particles in the fraction by dividing the sum of fluorescence intensity values of the fraction with the sum of light scattering intensity values of the fraction, and - monitoring and controlling the concentration of hydrophobic contaminants in the aqueous stream based on the calculated hydrophobicity density of the particles in the fraction. - adding together the fluorescence intensity values of the fractions thus obtaining a sum of the fluorescence intensity values, - adding together the light scattering intensity values of the fractions thus obtaining a sum of the light scattering intensity values, - calculating a hydrophobicity density of the particles in the sample by dividing the sum of the fluorescence intensity values with the sum of the light scattering intensity values, and - monitoring and controlling the concentration of hydrophobic contaminants in the aqueous stream based on the calculated hydrophobicity density of the particles in the sample, or - adding together the fluorescence intensity values of a fraction thus obtaining a sum of the fluorescence intensity values in the fraction, - adding together the light scattering intensity values of the fraction thus obtaining a sum of the light scattering intensity values in the fraction, - calculating a hydrophobicity density of the particles in the fraction by dividing the sum of fluorescence intensity values of the fraction with the sum of light scattering intensity values of the fraction, and - monitoring and controlling the concentration of hydrophobic contaminants in the aqueous stream based on the calculated hydrophobicity density of the particles in the fraction.