A submersed macrophyte index of condition for the Upper Mississippi River

- We developed a submersed macrophyte index (SMI) for the Upper Mississippi River.
- Four attributes were selected as metrics for the SMI.
- SMI scores increased downriver of Lake Pepin, which traps suspended solids.
- SMI scores decreased below navigation dams, which alter river hydrology.
- The SMI is the first macrophyte index for large rivers in North America.