Methylmercury is the most toxic organic form of mercury in the environment and humans are exposed mainly from the consumption of contaminated fish and shellfish. Methylmercury poisoning can cause adverse health effects including muscle weakness, disrupted motor function, and memory loss, and prenatal exposure can lead to problems with mental and motor development once a child is born. The utilization of the San Diego River in San Diego, CA for recreational and subsistence fishing has created a need for updated information on the human health risk posed by consumption of fish from the river. This study quantified the levels of Methylmercury found in four fish species (Micropterus salmoides or largemouth bass, n=20; Lepomis macrochirus or bluegill, n=11; Lepomis cyanellus, or green sunfish, n=4; and Ameiurus nebulosus or brown bullhead, n=3) from three locations on San Diego River. Muscle tissue analysis was carried out with a DMA-80 Direct Mercury Analyzer. Mercury levels from existing data for largemouth bass from El Capitan Reservoir was also used. A human health risk assessment was completed with data from this study and the El Capitan data set to calculate hazard quotients for 11 different scenarios for recreational and subsistence fishers in the San Diego River. Adverse health effects are likely to occur for recreational fishers who catch and consume maximally contaminated largemouth bass from El Capitan Reservoir, or all study species from the river at the rate of 17.5 g/day. Adverse health effects are also likely to occur for subsistence fishers who catch and consume only large mouth bass, a combination of large mouth bass and bluegill, or all study species from the river at the rate of 142.4 g/day. Additionally, adverse health effects were shown likely to occur for subsistence fishers who catch and consume largemouth bass from El Capitan Reservoir, however these risks are rare due to the financial burden associated with fishing at the reservoir. Overall, consuming fish caught from the San Diego River can be considered safe for recreational fishers, however subsistence fishers should limit their consumption to four 8-ounce servings of any species per week, or target only bluegill.