Fuxian lake (抚仙湖; fuxianhu) in Yuxi county, Yunnan province is one of deepest and cleanest lakes of China.
From Kunming or Yuxi take bus to Chengjiang city (澂江 or 澄江) to get North of the lake or bus to Jiangchuan (江川) to get to South end of lake.
Swim, camp, relax
By North and along West coast are villages with guesthouses and hotels. Around Luchong village (禄充村) is several five stars hotels under construction. East coast is without tourists (as well as shops!) and hills are great place to camp cause you have amazing view on sunset.