Abstract: Eutrophication has been recognized as a pollution p roblem all over the world. Blooms of the cyanobacterium are ubiquitous phenomena in eutrophic lakes and reservoirs in many countries. Although a number of published reports concer n cyanobacteria, the mechanisms governing the blooms are poorly understood. In pa rticular, nutrient dynamics are crucial in bloom processes, but they have mostly been addressed inadequately. Phosphorus is primarily responsible for limiting the growth of phytoplankton in freshwater systems. It is difficult to describe bl oomrelated processes without considering bioavailability of phosphorus in benthi c environments that act as sources of phosphorus. In addition, microbial degradat ion of organic matter is mediated by enzymes operating outside the cells. Extrac ellular phosphatase plays a key role in phosphorus regeneration. Thus, a study o n phosphorus status in benthic environments, including species and regeneration , is of ecological interest because of its implications for water blooms in the ecosystems. The phosphorus forms and kinetic parameters of alkaline phosphatase activity (APA) in the overlying, interstitial water and sediment, size-fraction ation of APA in overlying and interstitial water, as well as organic matter in t he sediments, were studied in adjacent ponds located in the eastern suburb of Wu han. Ponds with occurrence or bloom of Microcystis aeruginosa showed signifi cantly higher concentrations of orthophosphate (O—P) in overlying water, or dif ferent P species in interstitial water, whereas the pond void of Microcystis a eruginosa showed the lowest concentrations of chlorophylla in surface war er and different P species in overlying and interstitial water, indicating close relation between algae bloom and benthic phosphorus status. Sediment P was domi nated by Fe bound P fraction in all ponds studied. In the pond with heavily bloo m ofMicrocystis aeruginosa, the lowest Fe bound P and the highest organic m atter contents were observed in the sediment, coupled with the higher affinity f or the substrates (lowerKm values) and reaction velocity (higherVmax values) of APA in the bottom. These results suggested that organic matter may cau se anoxic status, and induce higher APA with different kinetic characteristics i n the overlying, interstitial water and sediment, thereby accelerating O—P rele ase and initiating bloom.