ZHOUTIE, China — By autumn, the stench of Lake Tai and the freakish green glow of its waters usually fade with the ebbing of the summer heat, but this year is different. Standing on a concrete embankment overlooking a fetid, floating array of plastic bottles, foam takeout containers, flip-flops and the occasional dead fish, Wu Lihong, the lake’s unofficial guardian, shook his head in disgust.