There are dozens of such reservoirs in the Sierra Nevada range in California. None of them will take as much water as Lake Mead, but they don't need to.
Sweden has lots of high mountains that may have shallow reservoirs built cheaply on top of. Reservoirs with earthen dikes are radically cheaper than the sort of dams needed for traditional hydro power, and may be placed almost anywhere, because they do not need or destroy a watershed. Lots of small ones, placed close to users, are better than one big one like Lake Mead.
Sweden has lots of high mountains that may have shallow reservoirs built cheaply on top of. Reservoirs with earthen dikes are radically cheaper than the sort of dams needed for traditional hydro power, and may be placed almost anywhere, because they do not need or destroy a watershed. Lots of small ones, placed close to users, are better than one big one like Lake Mead.