Fungi can affect aquatic ecosystems through syntrophic and parasitic interactions with other organisms and organic matter cycling, although food web theory has largely neglected the presence and role of them. In aquatic environments, some fungal parasites are known to not only reduce blooms of host phytoplankton, but also to contribute significantly to insusceptible zooplankton diet via consumption of parasite propagules — the so-called “mycoloop” pathway.  In particular, during phytoplankton blooms dominated by inedible phytoplankton, the mycoloop becomes critical for energy flow from autotrophs to zooplankton. Our group aimed to investigate how the mycoloop influences community dynamics in aquatic food webs by combining experimental and modelling approaches. We assembled an experimental system consisting of an inedible (host) phytoplankton species and its parasitic chytrid, an edible (non-host) phytoplankton species, and a zooplankton grazer. Parasitizing chytrids increased the abundance of edible phytoplankton, whereas zooplankton grazing decreased its abundance. In the presence of zooplankton and chytrids, competition effects between edible and inedible phytoplankton species depended on nutrient levels. At high nutrient levels, competition was balanced by an indirect positive chytrid effect and negative zooplankton grazing effects on edible phytoplankton. In contrast, at low nutrient levels, we found that chytrids had a negative impact on edible phytoplankton synergistically with zooplankton. We revealed for the first time experimentally that the mycoloop changed the effect of chytrids on edible phytoplankton from positive to negative depending on nutrient conditions. We also constructed mathematical models of the mycoloop web, consisting of one host and one non-host phytoplankton species, a fungal parasite and a zooplankton species consuming non-host phytoplankton as well as the parasite, under three different implementations of the host-parasite interaction. We analyzed the system dynamics for direct and indirect effects of the mycoloop for short-term dynamics, which were directly compared to corresponding experimental data, and also for long-term dynamics. We found that the interaction durability, delaying parasite production, supports bloom formation of host phytoplankton, thereby, strongly influencing short-term dynamics. Our study provides new insights on the role of fungi for phytoplankton bloom formation, especially during the early bloom stage.