The round goby (Neogobius melanostomus), an invasive species in the Great Lakes, accumulates harmful contaminants such as methyl mercury, due to its diet of zebra mussels (Dreissena polymorpha) and interaction with sediment. Methyl mercury's properties facilitate bioaccumulation in goby tissues, enabling trophic transfer to higher levels in the food web, potentially affecting significant fish species. Selenium, however, can reduce the bioavailability of mercury in the diet. A higher selenium-to-mercury ratio in tissues can mitigate mercury transfer. While mercury accumulation in round gobies has been documented in Lake Erie’s western basin, little is known about levels in the central basin. This study assessed mercury concentrations and selenium-to-mercury ratios in round gobies from Pennsylvania’s Lake Erie waters and tributaries. Round gobies were collected, euthanized, homogenized, and acid-digested for analysis. Mercury and selenium concentrations were measured using an inductively coupled plasma mass spectrometer (ICP-MS). Preliminary findings showed gobies from Presque Isle Bay had the highest mercury levels (up to 17.3 ng/g), while those from other areas exhibited lower levels. Analysis revealed a decline in selenium-to-mercury ratios as gobies increased in size, resulting in higher mercury bioavailability. This raises concerns for native game fish that prey on gobies, potentially leading to mercury accumulation and human health risks through fish consumption. These findings highlight the importance of understanding contaminant dynamics and trophic transfer in invasive species to protect aquatic ecosystems. Further research and management strategies are needed to address ecological and public health concerns linked to mercury bioaccumulation.