The Stream Reach

Stream Reach

The typical stream reach has riffles, pools and runs and should be perennial. The X-site (X) is the furthest downstream location, it is usually where the latitude and longitude readings are taken.

The reach is measured from this point upstream. Water samples and flow should be collected as close to the (X) as possible if suitable features are available. In high-gradient streams your benthic samples are collected from riffles/runs. Always move in an upstream directions so that your water and benthic samples are representative. For certain habitat conditions a right and left side is determined; this is done by looking downstream.


Most agencies that survey rivers and streams use 100-meters as the reach length. Volunteers are encouraged to use the same length but other lengths are also acceptable. Streams may meander and have thick vegetation so the entire length of the reach may not be visible. Under these circumstances the length of the reach can be reduced as a safety precaution, especially if younger volunteers are monitoring. If you reduce the size then your reach should have at least one riffle, run and pool if possible.

Additional Information

  • Stream Reach
    • Description: Stream reach diagram with additional information.
  • Perennial Stream
    • Description: A perennial stream or perennial river is a stream or river (channel) which has constant stream throughout the year through parts of its stream bed during years of normal rainfall.
  • Water Chemistry
    • Description: This section describes procedures and considerations for collecting water samples from wadeable stream reaches. For more information visit the programs overview of chemical integrity, or for more specific considerations regarding the design of a water quality monitoring program refer to the program’s Volunteer Manual.
  • Discharge Measurements
    • Description: The stream’s velocity (flow) is modified by conditions along and around the stream.
  • BMI Collection
    • Description: BMIs are animals without a backbone that can be seen with the naked eye, and have to the ability to cling to bottom surfaces such as rocks, leaves or roots. They include crustaceans, mollusks and annelids but in many aquatic environments most of the macroinvertebrate community are the larvae of aquatic insects.
  • Habitat Assessment
    • Description: The habitat evaluation process involves rating many different habitat conditions as optimal, suboptimal, marginal or poor based upon criteria (descriptions and a rating scale) included on the survey data sheets.