This study is the fourth component of the ëResearch on the environmental effects of the SIGMA plan: Effects of dredgings and harbour expansion on the environmentí This study concerns the monitoring of phytoplankton. Phytoplankton is an important component within the carbon cycle as within the food web. Total chlorophyll a can be used as a measure for the total phytoplankton biomass. Ecological modeling requires a subdivision of the total phytoplankton in `Diatoms fresh water, `Diatoms brackish water, `algae (remaining) fresh water and `algae (remaining) brackish water.