The water quality in Taihu Lake got worse from the 1990s to 2006, dropping to the lowest grade. During these years, the lake went from being a bit too rich in nutrients to having a medium level of excessive nutrients. Around Taihu Lake, the water quality in Changzhou City also deteriorated. Factors like industrial growth, urban development, and changes in farming practices played a big role in hurting the water quality. Additionally, poor management systems, a lack of focus on protecting the environment, and not enough sewage treatment capability were the main reasons for the lake's water quality problems.