China has planned 23 dams on the main stream of the Lancang (upper Mekong) River. The Chinese Government’s Thirteenth Five-Year Plan on Hydroelectricity Development (TFP) has goals to mitigate adverse effects on freshwater biodiversity. These measures are of international importance because China is the largest developer of hydropower projects. Herein we analyse the effects of the existing and planned dams on the fish fauna in the Lancang River. Drawing on development documents, the different types of mitigation measures on the proposed cascade of dams are assessed against the goals of the TFP. We find that: (1) migratory species (25% of total) are severely affected and there are few effective mitigation measures to conserve them; (2) a further 20% of species may be affected by lack of thermal pollution control or mitigation of peaking flow releases in the main stream; (3) fortunately, most species (81.14%) can be protected in tributary nature reserves in the lower Lancang, but many (54.4%) are inadequately protected in the upper Lancang; and (4) none of the 20 dams for which there is information meet all the five TFP conservation goals. There are lessons for mitigating the effects on biodiversity of Chinese-financed hydropower dams inside and outside China.