The River des Peres helped shape communities in the region after it formed during the Ice Age, when a wall of rock and ice blocked the Mississippi River and forced water to carve a new path. In the 1600s, the Kaskaskia and Tamaroa people settled along the river, and a few years later two Jesuit priests built a mission at its mouth that lasted only three years but gave the river its French name, meaning "river of the fathers." From the Ice Age until the late 1800s, the River des Peres was a curving stream through fertile prairies, and for nearly 800 years the Osage people stewarded the land along it before they were forcibly removed, severing many community members' connection to the waterway. The 114 square mile River des Peres watershed drains rainwater and snowmelt into the river, then into the Mississippi River and on to the Gulf of Mexico, so actions such as littering or cleaning up affect waterways both locally and downstream. Around Warson Park, native savanna, woodland, and riparian habitats provide food and shelter for wildlife, clean water and air, and are being restored by replacing invasive plants with native flowers and trees.