Harmful algal blooms (HABs) represent a natural phenomena caused by a mass proliferation of phytoplankton (cyanobacteria, diatoms, dinoflagellates) in waterbodies. Blooms can be harmful for the environment, human health and aquatic life due to the production of nocive toxins and the consequences of accumulated biomass (oxygen depletion). These blooms are occurring with increased regularity in marine and freshwater ecosystems and the reasons for their substantial intensification can be associated with a set of physical, chemical and biological factors including climate changes and anthropogenic impacts. Many bloom episodes have significant impacts on socio-economic systems. Fish mortality, illnesses caused by the consumption of contaminated seafood and the reluctance of consumers to purchase fish during HABs episodes represent only some of the economic impacts of HABs. The aim of this report is to evaluate the economic losses caused by HABs in different sectors. This was achieved by collecting data that exist in the technical literature and group them into four categories: (1) human health impacts; (2) fishery impacts; (3) tourism and recreation impacts; (4) monitoring and management costs. The data analysed refer to both marine and freshwater HABs. Among the sectors examined in this study, human health impacts appear less investigated than the other three categories. This is probably caused by the difficulty to assess the direct effects of toxins on human health because of the wide range of symptoms they can induce. Looking at the data, the interest in mitigating the economic losses associated with blooms is particularly demonstrated by studies aimed to develop monitoring and management strategies to reduce HABs episodes. Indeed, the water monitoring, when accompanied by appropriate management actions, can assure the mitigation of ongoing HABs and the reduction of negative impacts. During data collection, it has been more difficult to find economic data about blooms in Europe than in United States of America (USA). A reason may be the lack of European reports or publically available data about HABs and their socio-economic impacts. Much studies still have to be performed in this field, but the reported increase in HABs frequency will surely increase not only scientific analysis about HABs but also economic studies to report whether safeguards taken have succeeded in mitigating the economic impact associated with blooms.