According to results of investigations made from 1978 - 1985, the water level of Wulungu Lake had been dropping. lt was not until the end of 1987 when the Second Erdis River Diversion Project to replenish the lake water, was implemented that the water level of the lake began to be restored rapidly.

In July, 1987 and in July to August, 1989 the detailed investigation on the effects of water level changes on the aquatic vegetation and its environment, Was carried out. Results revealed that (1) the restoration of water level resulted in an increase in the aquatic vegetation coverage from 815 ha in 1985 to 4365 ha in 1989, and an increase in the total standing biomass from 7 700t to 41 750; of the aquatic vegetation; (2) among 53 species of vascular plants in the lake, reed (Phragmites communis Trin.) which was the most dominant species made up 68% of the total standing biomass and covered 81% of the total area of the aquatic vegetation. Potamogeton pectinatus and P. perfoliatus, the subdominant species, made up 11% and 8% of the total standing biomass respectively; (3) the vegetation was still in a process of rapid succession because the deeply-inundated reed was disappearing and the newly-formed plant communities in the shallow areas were developing. Under stable water level, the total area of aquatic vegetation would possibly decrease to about 3500 ha and the total standing biomass would possibly increase steadily year by year; (4) with a productivity of about 58 955t per year, it is apparent that the aquatic vegetation played an important role in the primary production and fishery of the lake. If if had not ben properly used the lake water would be organically polluted especially in area IV. Thus, periodic harvest is needed to remove products of aquatic plant from the lake.