Is there really a sewer system in the lake? Is that safe?

Yes. It's a uniquely engineered design that was installed in the 1920s before the lake was filled. Over 50 manholes were placed around the perimeter of the lakeshore, each leading to a system of large cast-iron pipes that are mostly buried in the lake bed. The system collects wastewater from over 600 homes and businesses and directs it to the sewer treatment plant just east of the dam. It's an elegant solution for the mountains because it utilizes gravity, and the wastewater cannot leak into the lake--the pressure of the lake water prevents anything from escaping the pipes. As the pipe joints deteriorate, however, lake water does leak into the system. In 2010 and 2011, a team of commercial divers sealed all the accessible joints and eliminated over half a million gallons a day of lake water leakage.