The Missouri River is now controlled by the Garrison Dam, which is approximately seven miles north of the park. Since the completion of the dam in the early 1950's, no large scale flooding has occurred in the area. Although this controlled watershed is good for humans living along the river’s edge, it has severe consequences for the natural environment. Many large trees such as cottonwood and willow rely on the flood for the perfect conditions for reproduction. This has created a false ecosystem which is resulting in a stagnant forest with little to no succession reminiscent of the historic “Lewis and Clark” forest. Fungus and Elm Diseases are also prevalent throughout the forest. Ongoing projects are working to save the forest and to allow future succession the opportunity to occur but many years of neglect and hardship have taken their toll on the existing system. Although the Missouri River is unlikely to flood, the Knife River is situated at a precarious location within the park’s borders. The Knife River flows through about three miles of the park and many of the archeological sites are located directly on the banks of this river. During the spring, huge ice dams will cause the river to rise over ten feet in an hour, when the dam breaks, ice and water scours the banks often resulting in entire banks being ripped from their berms. This in turn causes cultural sites to be lost or archeological artifacts left exposed to theft.