I know right where that lake is. The run-off from that lake formed the creek that ran right behind where they shot outdoors M.A.S.H., and that ran into a reservoir. Occaisionally, they showed the creek (often dry in the summer) in MASH TV shows. The reservoir was actually built by a bunch of rich Hollywood executives in the 1920s. They bought up the whole area as a private hunting reserve and club. They built that reservoir and stocked it with fish for private fishing. Many famous TV shows and movies were filmed at that reservoir including both scenes for Planet Of The Apes and David Carradine's Kung Fu in the 1970s. Caine and Master Po used to stand on a bridge the crossed over the reservoir wall.
But that club eventually was dissolved because there weren't enough people to afford the $200,000 / year membership fee so they sold the land to Fox Pictures and that became the Fox movie Ranch. Eventually in the late 70s, Fox donated the land to the state and it now stands today as Malibu Park. The end of that creek eventually flows south and empties out into the Pacific right near where they shot the outdoor scenes for the TV show Two and a Half Men.