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.