BIOLOGICAL ASSESSMENT While one can learn about the water quality in a given location by performing physical (i.e. pH, temperature, clarity) or chemical (i.e. salinity, levels of nitrogen or phosphorus) tests, these assessments typically require some expertise and equipment. An easier “first look” at a body of water is often a biological assessment—simply collecting a net sample of aquatic organisms to see what is living in the water. If there is good diversity and abundance of aquatic life, especially of those organisms that are sensitive to pollution, then it is reasonable to conclude the water is clean. A poor sampling suggests there is a problem, prompting one to look more closely at water quality to determine the reason for the problem.