The phosphorus fractions, the alkaline phosphatase activity (APA) and other water chemical parameters were concomitantly monitored from April 2003 to October 2004 in different ecotype sites of Lake Taihu. During the stages of algae growth, the phosphorus fractions and their relationships with APA in different ecotype sites were discussed and the phosphorus mineralization rate was calculated. In the water of Lake Taihu, most of the phosphorus (70.2%) could be attributed to the suspended particulate phosphorus, while the dissolved reactive phosphorus (DRP) seems to contribute less than 7%. About 58% of the total phosphorus, however, can be hydrolyzed as inorganic phosphate to compensate for phosphorus deficiency of algae and bacteria growth. During the different algae growth stages, the APA and its Kinetic parameters were varied significantly between different ecotype sites of Lake Taihu. This trend is also visible by comparing the phosphorus mineralization rate, and the most rapidly phosphorus turnover time is only several minutes. The fast recycle of phosphorus can, to some extent, be explained that the phosphorus source of algal blooms. The phytoplankton seems to compensate for phosphorus deficiency by using the alkaline phosphatase to hydrolyze phosphomonoesters.Phosphorus has been identified as the critical limiting nutrient for phytoplankton growth and production in many lakes, while the dissolved reactive phosphorus (DRP) generally was considered as the major fractions of phosphorus which can be directly used by phytoplankton [1,2] . Therefore, the phosphorus fractions, source and its relationship with algal blooms have been concerned, especially in the eutrophication lakes. At present, most of the researches concerning release nutrient from internal loading were concentrated on phosphorus concentrations characteristic of waters, nutrient concentration and release of sediments, the nutrient source-storage relationship and exchange on the water-sediment interface, etc. [3,4] . Study on some processes, such as the phosphorus recycles in the water, the nutrient compensate source during the algal blooms, would be helpful to understanding the nutrient recycle mechanism of water. Recently, there were several researches concentrated on the effects of bluegreen algal blooms to the phosphorus release from sediments [5,6] . In fact, it is difficult to get the relationship between the nutrient and algal bloom only by measuring the nutrient concentration of water. In order to better understand the nutrient status and the nutrient Alkaline phosphatase activity and the phosphorus mineralization rate of Lake Taihu 177 control phytoplankton production, the transport process of nutrient in different source of water should be considered.The main phosphorus fractions in water are dissolved organic phosphorus and sestonic phosphorus, which were ca. 12%-30% and 62%-82% of total phosphorus respectively. The DRP, which can be directly used by phytoplankton, was only ca. 5%-8% [7] . Although it has been claimed that bacteria are th...