Turbidity Tube

    Turbidity Tube

    Definition: Turbidity is a measurement of water clarity. Turbidity is the degree to which light penetration is blocked by Turbidity units and rangesuspended solids. Suspended solids are the materials suspended in the water (soil, sediment, algae, etc.) and affect how deeply light can penetrate.

    Why we monitor turbidity: Excessively turbid water can block sunlight, cause habitat loss, and make it hard for predators to find prey. Also turbid water can impact recreational water use. Sediments fill in spaces between cobbles that is important habitat for aquatic life and may smother fish eggs.

    What influences turbidity: Turbidity may be affected by seasons, such as increased runoff during snowmelt or large rain events. Human activities can increase erosion potential in the watershed and cause the turbidity to increase. Riparian plants along the banks play an important role to increase bank stability and reduce erosion. Large amounts of suspended plant materials such as algae may also increase turbidity.

    Conversion chart for Nephelometric Turbidity Units (NTUs) from centimeters (cms). 




    Dip tube into the water at your sampling site and fill to the top. Be care to sample flowing water and not the stream bottom. Do not stand upstream from the area you are sampling.

    Filling tube

    Take the reading in an evenly lighted area.


    Cover your hand over the top and shake the tube to resuspend any sediment. 

    Look through the tube toward the target disk on bottom.

    If the disk is visible, record the water level in centimeters.

    read disk

    If the disk is not visible, slowly release water from the valve until the disk becomes visible and then stop the valve.

    If it takes awhile to do this and sediment covers the disk then cover your hand over the top and shake the tube to re-suspend any sediment.

    Cover with hand

    Once the disk is barely visible, record the water level in cm on your datasheet.

    You can then use this table to convert to NTUs.

    Record tube reading

    Stream Side Science turbidity instructions - great for laminating and using with groups.


    Additional Resources: 

    Turbidity Test Educational Video from Envirothon 2016