The objective of this methodological paper is to outline a microscopy protocol for detecting and observing fungal zoosporic parasites of phytoplankton in natural environments, with potential applications in algal biotechnology to enhance the success and sustainability of algal cultivation endeavors. The fluorescent dual staining with wheat germ agglutinin (WGA) and Calcofluor White (CFW) showcased during the Training School "Identification and detection of zoosporic parasites" in Neuglobsow (Germany) from 16 th till 18 th of May 2023 and organized and funded by COST Action ParAqua (European Cooperation in Science and Technology) illustrated its ease of implementation and suitability for diverse natural and artificial systems.