Upper Mississippi River – Navigation and Ecosystem Sustainability Program Sny Magill Project

U.S. Army Corps of Engineers, St. Paul District
Published April 12, 2024


The Navigation and Ecosystem Sustainability Program, or NESP, is a long-term program of ecosystem restoration and navigation improvements for the Upper Mississippi River System.

The Sny Magill unit of Effigy Mounds National Monument is located within the floodplain of Pool 10 of the Upper Mississippi River between river mile 626 - 628 along Johnsons Slough.

The Sny Magill unit protects more than 100 Native American burial and ceremonial mounds, which are important to the 19 federally recognized tribal nations with which Effigy Mounds National Monument consults. The park and the tribal partners consider the mounds as unique and irreplaceable sacred cultural features of national significance.

The gravel outwash terrace underlying the mound group sits at a higher elevation than surrounding islands. Altered hydrology within the pool has created conditions during high water events that can undercut and/or saturate the substrate and cause bank failure. Several mounds have been damaged in past events. Previous National Park Service efforts to stabilize the eroding bank have had limited success. Prolonged high-water levels from 2018 to 2021 severely impacted the bank and six mounds are now in immediate jeopardy. Accelerated erosion and sedimentation may also be impacting vegetation and mussel communities within the slough.


This NESP study is a partnership with the National Park Service, U.S. Fish and Wildlife Service, Iowa Dept of Natural Resources, Wisconsin Dept of Natural Resources and the U.S. Army Corps of Engineers. The study will consider alternatives including riverbank stabilization and protection, floodplain restoration, closure or partial closure structures, and in-channel diversion structures.


The Project Implementation Report development through fall 2024 with public review period anticipated June/July 2024. Design is planned for 2025, and construction in 2026.


General Investigations - Title VIII of the Water Resources Development Act 2007


This project is expected to be constructed below the ordinary high-water mark; therefore, the construction of this project would be 100% federal and does not require a cost-share sponsor. Operations and Maintenance will be the responsibility of the project sponsor. Estimated total cost for planning, design and construction: ~$6 million.