During the Lewis and Clark Corps of Discovery expedition, the Missouri River was a wide, shallow river filled with islands, side channels, quiet backwaters, marshes, and a main channel, allowing the party at times to wade the river and pull boats upstream. Its floodplain was a mixture of grasslands, forests, and wetlands, and spring high water often flooded nearby land and deposited organic-rich sediments that supported productive plant communities, especially marshes that supplied important food for fish and other wildlife. Lewis and Clark also saw upland areas along the river marked by rock bluffs, and some historians believe a site a couple of miles downstream across the river on the St. Louis County bank was where Captain Lewis nearly fell from a bluff during the expedition's first few days. Seeking passage to the Pacific Ocean, they also recognized the river's value as transportation into the Great Plains and Rocky Mountains at a time when horses were the most common means of travel and waterways offered a fast, easy alternative for moving people and goods. Over time, the Missouri River changed significantly: formal exploration by Lewis and Clark in 1804-1806 was followed by snag removal in 1838 to promote steamboat traffic, the first government survey by Charles Howell in 1867, channel improvements funded by Congress from 1882 to 1902 that created a 5.5 foot deep navigation channel for the first 44 miles upstream to Augusta, construction of Fort Peck Dam beginning in 1933, the 1944 Flood Control Act's basin-wide Pick-Stone Plan that led to six additional dams, and the 1945 Rivers and Harbors Act, which established the present navigation channel at 9 feet deep and 30 feet wide and extended it to Sioux City, Iowa. Today the river has a very swift nine feet deep and 1000 wide navigation channel, roughly half its former width before channelization, dams and levees control most flooding, rich soils support productive agricultural land for Missouri farmers, blufftops are often valued as building sites with scenic views and flood protection, and the river still carries commodities such as Midwest grain and coal by barge.