In order to deal with cyanobacterial bloom occurred in Lake Taihu, a series of comprehensive measures have been carried out in Lake Taihu and surrounding catchment since 2007. In the current study, Meiliang Bay and Gonghu Bay was selected as study areas. For each bay, 3 sampling points were set for monitoring water quality twice a month since April 2010. The hydrological and meteorological data and water quality data from Wuxi Municipal Environmental Monitoring Station and Ministry of Water Resources Bureau of Taihu Basin were also collected. All the data showed that water quality in Lake Taihu was improving since 2010. The concentration of total nitrogen (TN) was decreasing year by year. Total phosphorus (TP) concentration has also been decreasing before 2014, but it started to increase in 2015 and 2016 ranging from 15 to 20 percentage. The increase of TP within 2015 and 2016 was due to two great floods occurred in both years, which brought large amount of nutrient into Lake Taihu. After the floods, most nitrogen was discharged away in soluble form while most phosphorous was gradually deposited in Lake Taihu as particulate form. The accumulated phosphorus was then released along with the consumption of dissolved total phosphorus, increasing pH and variation in dissolved oxygen due to Microcystis growth.