Although dams have some positive impacts on humans and some wildlife, there is an overwhelming amount of evidence demonstrating physical changes occurring in rivers caused by the destruction of river systems. More than 840,000 dams are operational worldwide, of which 80,000 are located in the United States. With so many dams in the world blocking free-flowing rivers; the impacts will certainly be significant. The harmful effects of dams can be minimized and in many cases reversed through dismantling obsolete or no longer productive dams and implementing a long-term monitoring plan with a focus on restoring river systems. Throughout this article I will also look at 2 dams in the United States, Shasta Dam and Hoover Dam. I will also look at the impact these dams have on the rivers they are blocking and how they physically change the river systems? I chose this topic because when I was a child camping near Lake Shasta with my family, my parents took my siblings and me on a tour of Shasta Dam. Even as a child, I knew that creating massive structures like this dam was an engineering feat, and I have been fascinated ever since. Here's a little background on dams as far as shape, size, and some of the effects they have on physically altering river systems, which we'll talk about later. There are several dams, but the four most common are gravity, arch, buttress, and embankment dams. The type of dam built depends on several variables: cost, purpose and size needed. There has not been extensive research into how dam style affects rivers compared to others, and this impact may be minimal. However, the size of the dam has notable effects that increase as you...middle of paper...go. With 85% of the world's dams in the large dam category exceeding their expected lifespan by 2020; the potential disaster if any of these dams were to break, it could not only destroy wildlife, kill humans, but once again physically change the landscape of the rivers as well. While dams have positive effects on humans in terms of recreation and hydroelectric power, there is an overwhelming amount of evidence that shows they do more harm than good, destroying riparian ecosystems and physically changing the natural flow of rivers permanently. . Let's work for a better tomorrow and repair the damage that has been done. The harmful effects that dams have on rivers by removing some dams that no longer meet certain operational standards, regulating better water flow and a better system to allow aquatic life and sedimentation to pass through.