Assessing Water Quality

[Adopted from Mauri Pelto at Nichols College]

We do need to take specific detailed water quality measurements to quantify the extent of water pollution issue. However, many water pollution issues can be qualitatively identified visually. Below are a series of videos of streams of varying water quality that emphasize key parameters to observe. In each stream we were also measuring the water quality quantitatively.


  1. What is covering the stream bottom?
    Lots of algae suggests high nutrient levels and low dissolved oxygen.
    Lots of moss indicates water that is relatively unpolluted.
    If the rocks are covered with a uniform coat of brownish material this is typically algae with sediment coating, often is a monoculture.
    Clean, bare rocks indicates an area of higher flow velocity, erosion and good water quality.
  2. Soapy bubbles or foam? Is there substantial foam on the surface of the water. It requires some degree of turbulence to generate, and if it persists and piles up, it is suggestive of high levels of nutrients, phosphates and nitrates.
  3. How clear is the water? If the water is not clear, it is likely due to either algae, eroded sediment, or substantial chemical pollution. Eroded sediment is typically limited to after rain events and turns the water a turbid brown from Latte to Cappacino colored. Algae is a lighter density and easier to suspend and just gives the water a darker brown or green cast. Water that is clear but has a bit of a yellow brown color-much like weak tea is clean. The color comes from tanic acid derived from forest litter decay. Other chemical pollution often gives the water a hazy appearance.
  4. Diversity of life? A diverse number of plants growing in the water and the associated insects and aquatic life is a good sign. If all you see is algae or a bottom that is a dark color with limited aquatic plant life that is not a good sign. If you look under rocks and see larvae of insects the more the merrier for water quality.
  5. Discoloration? There can be an oily sheen or a rusty cast to areas along the shore or bottom. The rusty color is often associated with algae and bacteria that capture iron, and can be natural in a region of rocks that are yielding considerable iron via weathering, but more often is not natural.Below is a growing list of examples for comparison.


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