Recent ecological research has increasingly focused on unraveling the complex dynamics of aquatic environments, particularly emphasizing the roles of micro-heterotrophs and the accessibility of organic matter to them. Heterotrophic bacteria, along with phytoplanktons in nutrient-deficient waters, stand as key players in aquatic ecosystems, exerting significant influence over nutrient cycling, organic matter transformation, mineralization, and energy flow. This chapter delves into the classification, localization, and ecological significance of microbial ectoenzymes, emphasizing their role in biogeochemical processes through enzymatic transformations and shedding light on their significance in mobilizing, transforming, and recycling both organic and inorganic constituents in aquatic ecosystems. The enzymatic mechanisms employed by micro-heterotrophs include the production of enzymes majorly hydrolytic, such as proteases, lipases, and carbohydrates, cleaving specific chemical bonds within organic molecules and transporting them into the cell for further metabolism. The dynamics of physicochemical parameters, such as pH, temperature, salinity, and nutrient availability, play a major role in microbial enzymatic activities across diverse aquatic environments. The dynamics of ectoenzymes in various aquatic niches, including marine, freshwater, and riverine systems, have been discussed in detail, highlighting the influence of factors such as nutrient availability, seasonal variations, and sediment characteristics on enzyme activity. It also discusses fluorometric assays and microfluidic methods for analyzing microbial extracellular enzyme activity, emphasizing the importance of accurate measurement techniques in ecological studies.