I'm friends with a retired professor who has actively opposed this project. He says that although the water from the Niulan River looks clean, it is actually very high in heavy metals - since there is a lot of industrial activity in the Songming/Qujing area. On the other hand, the water in Dianchi is still relativity low in heavy metals.

The algae blooms that riddle Dianchi are mainly caused from too much nitrogen input in the lake, stemming from fertilizer runoff and raw sewage. Nitrogen is not toxic per se, and if the inputs were curtailed then the algae blooms would diminish in due time.

But, heavy metals will last much longer in the environment and will bioaccumulate (become more concentrated higher up in the food chain).

Hopefully this provides a little food for thought. Clean-looking "fresh" water is not necessarily clean. Dirty-looking water may be much less dangerous than assumed. It seems that the local government is more invested in getting Dianchi to appear clean. At least this is my understanding. Please correct me if I'm wrong about anything.