Carthagena, Ohio is a small village located in Mercer County. The climate in Carthagena is classified as humid continental, characterized by warm summers and cold winters. The village is located near Grand Lake St. Marys, which is the largest inland lake in Ohio. The lake is a popular spot for fishing, boating, and other water activities. However, the lake and surrounding area have been impacted by algal blooms in recent years, leading to concerns about water quality. The main hydrology constituents in the area are the lake and several streams and wetlands. Overall, Carthagena offers opportunities for outdoor recreation and water-based activities, but visitors should be aware of potential water quality issues.