National Wetlands Inventory
Ecological Services

Surface Waters and Wetlands Product Summary

Product Summary iconThe SWI dataset is a more comprehensive characterization of all surface water features on the landscape. It stems from the need to represent all surface waters and wetlands as polygons in a geospatial dataset to facilitate accurate area calculations and provide consistent, standardized ecological classification to allow for adaptive management, geospatial summaries, and modeling. The SWI has been created by retaining the wetland and deepwater polygons that compose the NWI digital wetlands spatial data layer. The water bodies, already contained within the NWI data and classified as deepwater habitats using the Cowardin et al. (1979) nomenclature, are retained as they provided ecological descriptors of habitat types. These wetlands and deepwater features have been supplemented by reintroducing any linear wetland or surface water features that were orphaned from the original NWI hard copy maps and converting them to narrow polygonal features. The NWI wetland classification attribute is retained for these narrow features. Additionally, the data are supplemented with hydrography data as a secondary source for any single-line stream features not mapped by the NWI and to complete segmented connections. These features are assigned a Cowardin classification to conform to federal national mapping standards and buffered to become polygonal features as described above. A geoprocessing model addresses geospatial dominance issues, such as water bodies traversing through wetlands, and the translation of connecting NWI classified features with unclassified hydrography data. It also updates all existing NWI classifications to current standards. The resultant dataset is a more complete depiction of surface waters and wetlands. Due in part to how wetlands were mapped in the past, coupled with improved geospatial processing techniques, the SWI dataset is a departure from the legacy NWI data in several ways. The SWI depicts all surface water and wetland features in a single database; it applies the Cowardin et al. (1979) system to provide consistent ecological descriptors intended to address wetlands and water bodies; and it imparts new and improved information about wetland extent and hydrologic connectivity. The ramifications of generating the SWI data are substantial in terms of providing a more comprehensive inventory of wetland and associated water bodies. Recognizing the difference between these two datasets has implications for past wetland data summaries and modeling that has been generated using the legacy NWI map data.

  example of SWI mapping
Figure 1: An example of SWI mapping shows a composite of all surface waters and wetlands. Wetland polygonal features were retained from the NWI dataset (dark green) and combined with orphaned wetland linear features that were buffered to narrow polygons (light green) and hydrology linear segment connectors also buffered and assigned ecological classification (blue).

Explore the Surface Waters and Wetlands Inventory for Minnesota in the map below

Zoom to an area in Minnesota until the Surface Waters and Wetlands Inventory polygons draw.  Use the pan and zoom tools to navigate. Click on a specific polygon for more information.


Surface Waters and Wetlands Data Applications (Hydrology and Modeling)

There are many opportunities to apply SWI data to assist in resource management, planning, and strategic habitat conservation efforts. Applications include various geospatial analyses, tracing contaminant pathways through aquatic systems, identifying and prioritizing habitat restoration opportunities, examining continuity or dissection of habitat corridors, quantifying aquatic and wetland resource types, and facilitating ecological modeling. Modeling changes at the community level (e.g., species richness, diversity, cover, and biomass) are often linked to the hydrologic characteristics of wetlands or the surface water bodies adjacent to wetlands. Current hydrography that attempts to trace surface water flow is often incomplete or misleading because it lacks one or more of the landscape-level components that make up surface water features. The SWI dataset provides more complete geospatial data on surface waters and wetlands than has been available in the past and will provide a more efficient means to make determinations of flow and water movement in surface water basins and channels as well as in wetlands. The SWI database has been completed for over 15 states and will be publicly available in the summer of 2014 at

Please read the Disclaimer, Data Limitations, Exclusions and Precautions, and the Wetlands Geodatabase User Caution.

Last updated: January 19, 2016