• Chlorophyll is a specialized green pigment that enables plants to
• Plants, green algae and cyanobacteria all contain chlorophyll and can be found in lakes
• The health or productivity of a lake can be measured by how much phytoplankton is in the water.
• Scientists measure chlorophyll by shooting beams of light through the water and measuring how much of the light is absorbed by chlorophyll.

Plants contain a specialized pigment inside of the cell that enables the plant to use sunlight to make energy, or photosynthesize.  This pigment is called chlorophyll.  There are many different types of chlorophyll, just as there are many different types of plants in the lake.  When scientists want to figure out the productivity of a lake, they target a microscopic plant that floats in the water called phytoplankton.  There is a specialized probe that shoots a beam of light and takes a measurement of the amount of chlorophyll.  By measuring the amount of chlorophyll in the water, scientists can make a scientific guess (or hypothesis) as to how much phytoplankton is in the water.  If the lake has a high amount of phytoplankton, then it is probably healthy, too much or too little phytoplankton can indicate that the lake is in danger.  Certain types of pollution, like lawn fertilizers and sewage run-off, can cause big blooms of phytoplankton.  This can result in the phytoplankton forming a dense mat on the surface of the lake and shading everything below it from the sun.  Without sunlight, the other plants in the lake are no longer able to photosynthesize and they die, causing the organisms that depend on the plant’s supply of oxygen to die as well.  That is one of the reasons why it is very important that we are careful about what goes into our lakes.