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At the NWQL, Chlorophyll is determined as a means of assessing phytoplankton (single-celled algae) productivity in water and bottom sediment from lakes and streams. A sample of algae filtered from water or scraped from the bottom of the water body is extracted with a solvent, typically acetone. The extracted chlorophyll is measured by comparison to calibration standards using a fluorometer  that measures specific wavelengths of light emitted when the sample extract (or standard) is irradiated with a different specific wavelength range of light.