Aquatic vegetation in the Upper Mississippi River nearly collapsed in the late 1980 through early 1990. Looking for solutions, river managers began to evaluate with the US Army Corps of Engineers whether regaining some seasonal variability in water levels could regenerate the aquatic plant community. Historically water levels would rise in spring with snow melt and spring rains and fall off during the summer growing season and these seasonal changes create optimal conditions for plant germination and growth. Lock and dam operation maintains water levels higher in the summer months for commercial navigation, degrading conditions necessary to maintain plant communities.

The U.S. Army Corps of Engineers, St. Louis District and natural resource agency partners determined there was some flexibility in dam operations and depending on annual river hydrology the dams could be operated at the lower end of operational band. Initial demonstrations targeted a 30‐45 day window during the growing season to regain the annual aquatic plant community, essential for migrating waterbirds in the spring and fall. The demonstrations started in 1994 and continued through 2014 at Locks and Dams 24‐26.

A unique hydrological event in 2014 required the U.S. Army Corps of Engineers to maintain operation at the low end of operation for over 85 days. Not only did annual aquatic plant respond to the extended low water conditions but perennial aquatic plants reappeared, which had not been observed for over 20 years. With these observations, USACE and river partners decided to adapt this practice to hold water levels lower for an extended portion of the growing season (goal of 90+ days) if hydrologic conditions allowed. This change was implemented in 2015 and will continue through at least 2018. Response from these operational changes will be assessed to determine future implementation goals.