Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence (External Review Draft)

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The Environmental Protection Agency – through the independent Scientific Advisory Board (SAB) - is soliciting public comment on a new draft science report titled: Connectivity of Streams and Wetlands to Downstream Waters. A public docket has been opened to receive comments and those comments received by November 6, 2013, will be provided to the SAB Panel for its consideration in advance of their December 16- 18, 2013 meeting. Comments received after November 6, 2013, will be marked late and cannot be guaranteed to be provided to the Panel in advance of their meeting.

This draft science report presents a review and synthesis of relevant peer reviewed scientific literature that will inform an upcoming joint USEPA/ Army Corps of Engineers rulemaking to enhance protection of the chemical, physical, and biological integrity of our nation’s waters by clarifying Clean Water Act (CWA) jurisdiction. Recent decisions of the Supreme Court have underscored the need for EPA and the public to better understand the connectivity or isolation of streams and wetlands relative to larger water bodies such as rivers, lakes, estuaries, and oceans, and to use that understanding to underpin regulatory actions and increase certainty among various CWA stakeholders. This report, when finalized, will provide the scientific basis needed to clarify CWA jurisdiction, including a description of the factors that influence connectivity and the mechanisms by which connected waters affect downstream waters.

This draft science report represents the state-of-the-science on the connectivity and isolation of waters in the United States. It makes three main initial conclusions, summarized below, that are drawn from a broad range of peer reviewed scientific literature.
  • Streams, regardless of their size or how frequently they flow, are connected to and have important effects on downstream waters. These streams supply most of the water in rivers, transport sediment and organic matter, provide habitat for many species, and take up or change nutrients that could otherwise impair downstream waters.

  • Wetlands and open-waters in floodplains of streams and rivers and in riparian areas (transition areas between terrestrial and aquatic ecosystems) are integrated with streams and rivers. They strongly influence downstream waters by affecting the flow of water, trapping and reducing nonpoint source pollution, and exchanging biological species.

  • Finally, there is insufficient information to generalize about wetlands and open-waters located outside of riparian areas and floodplains and their connectivity to downstream waters.
Through public comment and independent peer review by the SAB, the agency is seeking input concerning the literature summarized in the report and the strengths of its conclusions. As a result of that input and review by the SAB external review panel, the agency will consider revisions to these conclusions as it prepares its final report.

In addition to the release of this report, EPA, with the Army Corps of Engineers, has sent a draft rule to clarify the jurisdiction of the Clean Water Act to the Office of Management and Budget for interagency review. This draft rule takes into consideration the current state-of-the-art peer reviewed science reflected in the draft science report. Any final regulatory action related to the jurisdiction of the Clean Water Act in a rulemaking will be based on the final version of this scientific assessment, which will reflect EPA’s consideration of all comments received from the public and the independent peer review.

The proposed rule is limited to clarifying current uncertainty concerning the jurisdiction of the Clean Water Act that has arisen as an outgrowth of recent Supreme Court decisions; it does not propose changes to existing regulatory exemptions and exclusions, including those that apply to the agricultural sector that ensure the continuing production of food, fiber and fuel to the benefit of all Americans. Specifically, EPA and the Army Corps are interested in enhancing the ability of the CWA and USDA's conservation programs to work in tandem to protect water quality and improve the environment by encouraging expanded participation in conservation programs by farmers and ranchers. It will do so by providing greater clarity on which waters are not subject to CWA jurisdiction and greater certainty on which activities do not require CWA permits.

Current activities and waters falling under existing agricultural exemptions from Clean Water Act jurisdiction or permitting:

Exemptions from Clean Water Act permitting continue for:
  • Agricultural stormwater discharges.
  • Return flows from irrigated agriculture.
  • Normal farming, silvicultural, and ranching activities.
  • Upland soil and water conservation practices.
  • Construction and maintenance of farm or stock ponds or irrigation ditches.
  • Maintenance of drainage ditches.
  • Construction or maintenance of farm, forest, and temporary mining roads.
Exclusions from Clean Water Act jurisdiction continue for:
  • Prior Converted Cropland, including the role of USDA.
  • Waste Treatment Systems.
The proposed rule submitted to OMB for review includes exclusions from Clean Water Act jurisdiction for:
  • Non-tidal drainage, including tiles, and irrigation ditches excavated on dry land.
  • Artificially irrigated areas that would be dry if irrigation stops.
  • Artificial lakes or ponds used for purposes such as stock watering or irrigation.
  • Areas artificially flooded for rice growing.
  • Artificial ornamental waters created for primarily aesthetic reasons.
  • Water-filled depressions created as a result of construction activity.
  • Pits excavated in uplands for fill, sand, or gravel that fill with water.

This draft science report presents a review and synthesis of the scientific literature pertaining to physical, chemical, and biological connections from streams, wetlands, and open-waters to downstream waters such as rivers, lakes, estuaries, and oceans. This review of more than 1000 peer-reviewed publications summarizes the current scientific understanding of the connectivity of small or temporary streams, wetlands, and certain open-waters, evaluated singly or in aggregate, and the mechanisms by which they affect the function or condition of downstream waters. The goals of the report are to (1) provide a context for considering the evidence of connections between rivers and their tributary waters, (2) summarize current understanding about these connections and associated downstream effects, and (3) discuss factors that influence the degree of connectivity or the magnitude of a downstream effect.


This report provides a review and synthesis of the scientific evidence pertaining to physical, chemical, and biological connections from streams, wetlands, and open-waters to downstream waters such as rivers, lakes, estuaries, and oceans.


Following external review by the SAB and consideration of public comments submitted, the EPA will revise the document and publish it as a final report on the EPA website.


U.S. EPA. Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence (External Review Draft). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-11/098B, 2013.


Date Description
04-Sep 2013EPA released a draft report for external public review (via the Science Advisory Board) and invited submission of public comments for consideration by the SAB.

Additional Information

Comments for the SAB review panel’s consideration may be submitted and reviewed using the e-Government website. From the site, select “Environmental Protection Agency” and the keyword “EPA-HQ-OA-2013-0582” (for the docket ID) to submit comments.