Invasive plants are introduced into foreign ecosystems and proliferate easily. These plants often have no natural consumers in their new environment, allowing them to outcompete neighboring native plants, causing a plethora of detriments. This research aimed to help solve a rarely investigated aspect of this problem: the effect of invasive plant leaf litter on lake ecosystem dynamics. It was predicted that invasive leaf litter would have more adverse effects on a lake than native litter, because overwhelming evidence in the literature indicates the harm of invasive plants. This was tested with four groups of mesocosms corresponding to four leaf litter treatments: a native mix of red maple and American beech litter, a monoculture of invasive common reed leaf litter, an invasive monoculture of Japanese knotweed litter, and a mixture of litter from all four species. Using repeated measures analysis of variance statistical tests, each treatment was compared in its effects on the lake ecosystem’s phosphate concentration, nitrate concentration, algae growth, mosquito development, pH, dissolved oxygen concentration, and water conductivity. The common reed leaf litter treatment resulted in the highest nitrate, phosphate, and oxygen levels, leading to the conclusion that this leaf litter can potentially cause eutrophication in lakes. Additionally, Japanese knotweed resulted in the highest conductivity and lowest oxygen levels, showing its leaf litter has the fastest breakdown. The rapidity of this breakdown poses a harm to a lake as adjustment to rapid changes places various stresses on ecosystems. These discoveries can be implemented in lake conservation to more effectively maintain a healthy ecosystem.