Physical Evaluation

This portion of the survey includes a wide variety of observations using all senses, making several judgments based on established rating descriptions, as well as collection and measurement procedures. In this section we discuss general physical observations. These observations should be completed prior following the water quality analysis. The table below provides a list of the conditions that are assessed as wells as some general guidelines regarding what certain characteristics indicate. Water observations are made in a run or riffles, sediment observations are also made in a run or riffle and benthic algae observations are made in a riffle. These observations should be made multiple times throughout the reach to make sure conditions are consistent. You should write comments on the survey data sheet if any notable differences within the reach are observed. The University of Maine's field guide to aquatic phenomenon provides an overview and images of many of the conditions below.

Water Conditions


  • Brown - Usually caused by sediment in the water. Some muddiness (brown color) is natural after storms, but if the condition persists look for an activity upstream that has disturbed the soil such as construction sites, logging, storm water runoff from roads or urban areas, or agricultural activities such as cattle in the stream.
  • Black - Usually caused by coalmine drainage, tar or sometimes waste material from road construction.
  • Green - Often due to an algae bloom caused by excessive nutrients in the water. The source could be sewage, fertilizers from farms, homes or golf courses or waste from animal feedlots.
  • Multi-Colored Sheen - Can occur naturally in stagnant waters, but a sheen that is moving or does not break up easily may be an indication of oil pollution. The source could be runoff from streets or parking areas or illegal dumping. In some areas the use of all-terrain vehicles may contribute to stream oil pollution.
  • Orange or Red - Often associated with acide mine drainage.
  • Tea Colors - Caused by wetlands or tanins.
  • White or Gray - Can be caused by runoff from landfills, sewage, and mining.


  • Rotten Eggs - This strong sulfur-like odor can be an indication of sewage pollution or polluted coalmine drainage.
  • Musky - This slight organic odor is often natural, but in some cases may indicate nutrient enrichment from organic waste products or sewage contamination.
  • Oily - This odor may indicate pollution from oil and gas wells.
  • Chemical - There are a wide variety of chemical odors usually the result of industrial discharges, solvents and detergents.

Substration Conditions


  • Brown - Indication of silt deposits from sediment sources. Most stream bottoms are normally brown in color.
  • Black - Black deposits can occur naturally in heavy organic soils but can also be due to fine coal particles, tars, ashes, sludge etc.
  • Green - A possible indication of excessive algae growth from organic (nutrient) enrichment sources.
  • Orange or Red - Coating of flocculates on the sediments is usually due to polluted coalmine drainage.
  • White or Gray - Cottony mass is a sewage fungus common to organic polluted waters. An even coating of white or gray flocculates may be aluminum precipitating out of solution from acid mine drainage.


Volunteer monitors do not assess sediment odors; but occasionally it is good practice to compare sediment odors to odors in the water column. Stirring the bottom sediments and collecting a sample of water and sediment near the area that was disturbed assess sediment odors. The odors in the sediments are similar to those described for water.

Streambed composition is either estimated or measured using a pebble count procedure. The major size categories are silt/clay (mud), sand, fine gravel, coarse gravel, cobble, boulder, bedrock and woody debris. Read the pebble count section for more information.

Algae Conditions


Algae color varies from brown to dark green in most streams and rivers; although color is a noticeable condition of the algae it is not a particular indicator of the types or of the condition represented by the algal community.


Coverage in a riffle is estimated based upon the following: none, scattered, moderate or heavy. A heavy coating of matted and floating algae is often an indication of nutrient rich conditions caused by excess nitrogen and phosphorous.

Growth Habit

The growth habit characteristics are critical to understating the algae. Most stream algae will be evenly coated on the rocks and have a smooth or slimy texture; other types will be filamentous and have a hairy texture; and others will be matted. Matted algae are easily removed from the surfaces by slowly scraping with your fingers. If the algal community is mostly matted pieces will come off in junks like carpet when it has been removed from flooring.

Foam occurs naturally due to the decomposition of leaves (this foam is generally less than three inches high and cream colored). Excessive white foam may be due to detergent pollution.


  • Benthic Algae

    Benthic stream algae distribution and structure presented by Chritopher Eisler of Tennessee Tech. University.

  • A Field Guide to Aquatic Phenomena

    Lakes and streams don't always look or behave the way we expect. Water can be full of strange colors, unidentified blobs, and swimming creatures.

  • Acid Mine Drainage

    Acid mine drainage (AMD) is water contaminated when pyrite (iron sulfide) is exposed to air and water. The exposure often results in reactions that form sulfuric acid and dissolved iron. Some or all of this iron can precipitate to form the red, orange, or yellow sediments (yellowboy) on the streambed.

  • Pebble Count

    The composition of the streambed and banks is an important facet of stream character, influencing channel form and hydraulics, erosion rates, sediment supply, and other parameters. Observations tell us that steep mountain streams with beds of boulders and cobbles act differently from low-gradient streams with beds of sand or silt.

  • Foam

    Foam often is seen accumulating against logs or on the banks of streams, or along the shores of lakes on windy days. When it first appears, foam can be white, but generally turns brown over time. The development of foam occurs due to changes in the water surface tension and the physical introduction of air.