All lakes die. Vegetation grows along the edges and dies and decays, leaving organic sediment on the bottom on the lake. The edges of the lake creep inward.
Sometimes, sediment washes into the lake and fills it. This is the case with Alton Lake, Pool 26 on the Upper Mississippi River. The system of locks and dams on the Upper Mississippi, which turned it into a profitable navigation channel, turned each of the pools that formed behind the dams into lakes.
Sediment washing from the surrounding uplands is filling the Alton Lake and its backwaters, like Brickhouse Slough and the interior sloughs of Dresser Island. Floods wash more sediment onto the the island.
Before we built the dams, floods would flush sediment from the sloughs. Now only the biggest flood is capable of removing sediment from the sloughs.
Hence, when the Corps of Engineers decided to restore Dresser Island they encircled it with a levee to keep sediment-laden water off the island and out of the interior sloughs and designed water control structures to introduce fresh water into the sloughs, including Brickhouse Slough.