Final answer:
South Dakota is the state with the 4th largest reservoir in the US, Lake Oahe, in addition to Lake Francis Case and Lewis and Clark Lake. The largest is Lake Mead, behind the Hoover Dam. The Fort Peck Dam in Montana also created one of the world's largest man-made lakes.
Step-by-step explanation:
The state that has the 4th largest reservoir in the US, Lake Oahe, Lake Francis Case, and Lewis and Clark Lake, is South Dakota. While Lake Oahe is the 4th largest reservoir, the largest reservoir in the US is Lake Mead, created by the Hoover Dam in Nevada. The creation of these man-made lakes is a result of large-scale engineering projects like the Fort Peck Dam in Montana. The majority of freshwater is contained in glaciers and ice caps, indicating that despite the large volumes in reservoirs, much of Earth's accessible freshwater is locked in frozen form.