This map displays the pattern of different surface water feature types across the
state of Wyoming, including perennial, intermittent and ephemeral streams.
Perennial streams generally contain water throughout the year, except for periods
of extreme drought. Intermittent streams contain water for only part of the year,
while ephemeral streams flow only in response to precipitation events. Although
the intermittent and ephemeral stream classifications are distinguished from each
other in the dataset, many ephemeral streams are included in the "intermittent"
category. In addition, some ephemeral streams in the Southwest have been
classified as washes. Only recently, and mainly on U.S. Forest Service land, have
streams been added to the dataset under the "ephemeral" category, so very few
streams are indicated as such. The map highlights the predominance of
intermittent and ephemeral streams across the state. Of the 269,872 miles of linear
streams in Wyoming, 83 percent (224,249 miles) are intermittent or ephemeral.
Three percent of streams are ditches (9,301 miles), which are not classified by
their flow duration in the dataset.
The water features on the map are from the National Hydrography Dataset (NHD)
at high resolution (1:24,000 scale or higher) (data current as of October 2009).
Many smaller waters are not included in the NHD because they could not be
detected on the original aerial photos used to create the dataset or were excluded
from the maps from which the dataset originates. The majority of perennial and
most intermittent streams are captured at this resolution. However, most
ephemeral streams are not captured unless they are in the arid west. Additional
information on the NHD can be obtained from the NHD website at
https://nhd.usgs.gov.
^USGS
science for a changing world
l mi
Streams and Waterbodies in Wyoming
The National Hydrography Dataset
This map relies exclusively on USGS data for mapping water resources such as streams and other waterbodies. Due to the resolution of the map, it does not distinguish effectively between land and water and thus
makes waters appear more prevalent than is actual. This map does not depict the scope of waters protected under the Clean Water Act or the scope of waters that would be protected under the Army/EPA proposed
rule. This map has not been used for any regulatory purpose.
SURFACE WATER FEATURES
~	STREAM/RIVER - PERENNIAL
~	STREAM/RIVER - INTERMITTENT
~	STREAM/RIVER - EPHEMERAL
~	STREAM/RIVER - UNCLASSIFIED
~	CANAL/DITCH
O LAKE/POND OR RESERVOIR
H SWAMP/MARSH
~	PLAYA
~	WASH
0 STATE BOUNDARY
0	25	50	100
Miles
Prepared by INDUS Corporation under contract with
U.S. Environmental Protection Agency
Office of Water - Washington, DC
October 2013

-------