Los Angeles Department of Water & Power chief David Nahai has resigned to take a post as senior advisor to the Clinton Climate Initiative, Mayor Antonio Villaraigosa announced Friday.

The Clinton Climate Initiative is an arm of the William J. Clinton Foundation launched to address the issues of climate change and greenhouse gas emissions. It focuses on increasing energy efficiency in cities, developing sources of renewable energy and limiting deforestation. The Clinton Foundation has offices in Boston, New York and Little Rock, Ark.; it was not clear Friday where Nahai will be based.

Nahai, 57, took over as general manager of the DWP in late 2007 following the illness of Ron Deaton. He immediately faced a tough campaign to pass a hefty water rate increase and led an unsuccessful attempt to pass a bond measure for solar power projects.

Nahai has focused the agency on expanding its portfolio of renewable power to meet a Villaraigosa goal of being coal-free by 2020. Recently, the DWP has taken some heat over a rash of water main breaks that has exposed how far behind the agency is in maintaining its aging infrastructure.

Prior to being named general manager, Nahai served as Villaraigosa’s appointee on the DWP board. Before that, Nahai served as chairman of the Los Angeles Regional Water Quality Control Board. Prior to entering public service, Nahai, an Iranian immigrant, headed up his own law firm specializing in environmental law and real estate.

No replacement has been named; however, there was speculation Friday morning that Villaraigosa would name his deputy mayor for energy and environment, David Freeman, as interim general manager. Freeman headed the DWP during the second term of former Mayor Richard Riordan, from 1997 through 2001.