斜阳下，湖若明镜，波光辉映。 The lake is a like a brilliant mirror, the shimmering water reflecting the rays of the setting sun. With the shimmering reflection under the setting sun, the lake is like a brilliant mirror. The shimmering water of the lake reflects the rays of the setting sun like a brilliant mirror.

yeah，Thank you for your opinion，I think it is very reasonable. I revised my friend's long Chinese sentence to make this sentence，so I don't think about the meaning too much. You are right, if the lake is like the mirror, there would be no wave. Maybe the sentence should be 斜阳下，湖若明镜，辉映山色，：P。

"The lake is like a bright (or brilliant) mirror, reflecting the glistening light of the setting sun." Or, "...reflecting the sparkling radiance of the setting sun". You could use Panther's word "shimmering" if the water was moving. But if the water is like a mirror, then it is probably flat, not shimmering or moving. If the water IS moving (shimmering), then it is not like a mirror. But it's like poetry, so you can express it however you feel it. :-)