Quantifying concentrations and contributions of carbon species is an important part of building comprehensive regional and global carbon (C) budgets necessary for understanding climate change. Until recently, inland waters have been ignored in C budgets. Recent research suggests that although inland waters make up a small fraction of the Earth's surface, they are important in the global C cycle. We examined and related limnological, meteorological, and catchment land-use data to partial pressures of carbon dioxide (CO2) in 131 agriculturally-eutrophic lakes. We also examined carbon fractions in 15 agriculture-dominated catchments over an 11 year period to address how C is related to land-use and climate characteristics. In contrast to previous analyses, we found that our lakes were under saturated with CO2 and showed that variability in CO2 was related to nutrient-driven primary production. We found that C fractions in streams were related to discharge and that total C flux increased by several orders of magnitude with discharge.