Harmful algal blooms negatively impact freshwater, estuarine, and marine systems worldwide, including those used for drinking water, recreation, and aquaculture, through the production of toxic and non-toxic secondary metabolites. Consequently, water resource managers often utilize chemical, bacterial, physical, and plant-based treatments to control algal blooms. In aquaculture, copper sulfate, one of the only two approved algaecides, is commonly used because of its relative inexpensiveness and ability to quickly reduce algae. However, awareness or availability of alternative treatments may be limited due to disagreement among algal bloom treatment effects across studies, especially when comparing lab and field experiment results. Such variation within the literature and lack of knowledge of other tested treatments leave uncertainty for water resource managers when deciding what treatments to use to control harmful algal blooms. The objective of this research was to synthesize published and unpublished data from 39 studies that used one of 28 chemical, bacterial, physical, and/or plant-based algal bloom treatments used in field experiments on various algal measures (i.e., phytoplankton pigments and cell density, microcystin, and off-flavors). Overall, only a handful of chemicals, including copper sulfate, hydrogen peroxide, peracetic acid, and simazine, mediated algal blooms either measured at the day of most significant algal decline following treatment or at the end of the experiment. None of the bacterial, physical, or plant-based treatments were shown to significantly control algal blooms, toxins, or off-flavors by themselves. Results from this synthesis quantitatively showed that most treatments for algal blooms do not significantly improve water quality and highlight the need for more research on alternative treatments