All lakes die. Vegetation grows, dies, decays, and fills the lake bottom with organic matter. In the 1930s the Army Corps of Engineers built 26 dams on the Upper Mississippi, turning what had been a free-flowing river into a series of lakes, which received a double whammy. Decayed vegetation filled the lake bottoms and tributaries to the Upper Mississippi delivered sediment, washed down from the uplands which the river could not move downstream. It backed up behind the dams.
Not as dramatic as the Yellowstone Gorge, but the Upper Mississippi Gorge flows through a classic v-shaped gorge, lined with sedimentary rocks rather than igneous rocks. Between the bluffs the Upper Mississippi streams through a massive wetland. In 1922 Will Dilg, founder of the Issac Walton League protested the draining the wetlands of the Winneshiek Bottoms for farmland. In 1924 he succeeded in lobbying the U.S. Fish and Wildlife Service to create a refuge along the river between the mouth of the Chippewa and Rock Island, Illlinois.
People don't realize it, not even those who live along the Upper Mississippi River, but it is a national park.
North of the Chippewa, wetlands are found in state or county refuges. Catherine Pass lies in the Pierce County Wildlife Refuge in Wisconsin, where ducks rest on their annual migrations. To give them a chance to rest at Catherine Pass, the refuge does not allow duck hunting during migration season.
While the construction of dams on the Upper Mississippi broke the river into a series of pools and changed the nature of the wetlands. While the northern end of each pool resembled the old river, though at times the pools could be too deep for wetland plants to grow. At the southern end sediment pouring into the river from its tributaries backed up behind the dams and clogged the pools.
Hence, the Iowa River delivers more sediment to the Winneshiek Bottoms than the river can handle and mud flats build up and water lilies choke Henderson Slough at the southern end of Pool 13.
Lilies grow in Potter's Marsh, where silt decayed vegetation has filled the river bottom above Dam #13.