Cyanobacteria, a type of algae, proliferates every year upstream Dongjiang, a river in Guangdong province. A Hong Kong academic blames the algae growth on the heavy erosion brought about by widespread timbering in the city of Huizhou. Since the 1980s, this cycle has perpetuated: slash and burn vegetation, plant eucalyptus, chop down the trees for paper manufacturing. However, eucalyptus tends to loosen surface soil which ends up in the river as a continuous supply of nutrients for the growth of algae. The Pearl Report scrutinises the competing interests of ecology and economy. Reporter:Stuart Lau/Diane To