Microcystis aeruginosa is a unicellular, colonial cyanobacterium that produces a potent class of hepatotoxins called microcystins (MCs). During harmful algal blooms (HABs), Microcystis populations can drastically increase and release substantial quantities of microcystins into the surrounding waters upon cell death. These toxins can compromise environmental and human health. Therefore, it is important to understand what factors inhibit or stimulate Microcystis growth. In this study, Microcystis cultures were exposed to Roundup (glyphosate), bisphenol A (BPA), Diuron, and lab-created microplastic solution in a 96 well plate. Growth of the cultures were tracked daily by measuring the absorbance of chlorophyll in each well with a spectrophotometer. After three days, treatments that exhibited substantial growth inhibition or stimulation from the control group were scaled up to 250 mL flask exposures. A more concentrated microplastic solution was created for the flask exposure in order to explore the effect of a more concentrated exposure. The results of this study revealed that exposure to Diuron severely inhibited the growth rates of Microcystis. BPA and glyphosate inhibited growth in the well plates, but stimulate growth in the 250 mL flasks. Exposure to the microplastic solution inhibited growth more severely in the flasks than in the 96 well plate.