California’s aquatic environment is prone to mercury contamination due to historic and current mining processes, where mercury is used to purify gold. As mercury leaches from mining sites and into water, it converts into highly toxic methylmercury and bioaccumulates in fish from their food or as water passes through their gills. As a result, many of California’s lakes and rivers have fish-consumption advisories. Eventually, continued accumulation will lead to illness and death in fish. To combat this, I propose ProTP6, a probiotic for fish. The probiotic will contain L acidophilus genetically modified with the plasmid pTP6 derived from C. metallidurans strain MSR33 using electroporation. The genes in pTP6 code for proteins that reduce mercury ions, thus rendering methylmercury harmless. The engineered bacteria will be preserved in 10% DMSO, then freeze-dried and broken into pellets or a powder. The probiotic can then be applied to water bodies, where the pellets will be taken up as food and the powder will latch onto the gills and skin of fish. From then on, the bacteria will grow and protect the fish hosts against mercury contamination in the water. ProTP6 is a safe, sustainable, and cost-effective solution to mitigating mercury bioaccumulation.