Following the SWANCC decision, federal agencies, states, scientists and various interest groups became engaged in a series of scientific evaluations and analyses of the extent and importance of the isolated wetlands as well as headwater streams and their adjacent wetlands in achieving the goals of the Clean Water Act.

To understand the importance of headwater streams and wetlands it is important to understand and visualize a watershed. A watershed is a series of smaller streams draining into larger ones that can be pictured as a tree stretching over the landscape. The trunk is the major river flowing to the sea. The branches are major tributaries flowing to the trunk (for example the Ohio and Missouri rivers are tributaries (branches) to the Mississippi (trunk). Streams flow into streams that flow into streams. High up in the watershed, the area called the headwaters, streams are very small. A tree has many more small twigs and leaves than large branches. A watershed is like this as well. So it is logical that headwaters make up most of the tree. The tree dies if all the twigs and leaves are removed. A river becomes degraded if there is extensive alteration and change in its small tributaries. Based on this tree analogy there would many more stream miles of these small streams (twigs) than major streams and rivers (large branches and tree trunk). It is possible to imagine the leaves on the tree as small wetlands, but here the tree analogy falls short since there are also extensive wetland systems associated with major rivers.

Over the past couple of years, EPA has gathered information to assess the potential impact if a Supreme Court decision removed headwaters, small streams and wetlands from the CWA jurisdiction. ASWM queried EPA and received the following information quantifying the importance of these waters.

In a letter to ASWM dated January 9, 2006 EPA Assistant Administrator for Water, Ben Grumbles stated: that 40% of the point source discharges permitted under Clean Water Act (excluding stormwater and nonstormwater general permits) were located on intermittent, ephemeral or very small perennial streams. In addition 90% of the source water protection areas providing drinking water for over 110 million Americans were located in the headwater areas of watershed in the U.S. (excluding Alaska). The complete letter is available HERE.

These estimates as well as the information displayed on the maps and charts below represent a very conservative estimate of headwater areas in the U.S. The only national resource available is the National Hydrographic Dataset (the blue lines on USGS topographic maps). There is no direct way to derive "headwater areas" from the National Hydrographic Dataset (NHD) and EPA prepared its conservative estimate by mapping all intermittent and ephemeral steams contained in the NHD and the "start reaches", segments of perennial streams (those without other streams flowing into them), to develop a national and state by state estimate of headwater areas. In a second letter, dated January 11, Ben Grumbles provides a detailed description of how EPA developed this information. See [[HEADWATERS LINK]]. Individual states conducting similar analyses with better information may determine that the percentage of headwater areas in their states is in fact higher, and therefore the percentage source water protection areas for drinking water and point sources discharges regulated under the Clean Water Act in headwaters may be higher.

The following maps show the extent and concentration of intermittent, ephemeral and headwaters in the U.S. using the National Hydrographic Dataset:

Intermittent/Ephemeral Streams

Headwater Streams

The following maps display the same information for the State of Michigan:

Headwater Streams in Michigan

Intermittent and Ephemeral Streams in Michigan

Michigan Streams

A state-by-state breakdown of some of this information was also provided by EPA. The table identifies the extent of intermittent/ephemeral streams in each state and the population/drinking water systems dependent on these headwater areas as source of drinking water.   This table is in PDF format and may be viewed and/or downloaded by clicking HERE.