In this study, we have analysed the series of daily air temperatures from 1977 to 2009 measured in a sedge-grass marsh ecosystem near the town of Třeboň, Czech Republic (Central Europe). Annual averages of daily mean, minimum and maximum temperatures were analysed. Possible significant increases were recorded for all these values during the study period. The annual average of daily maximum temperatures increased on average by 0.0827 °C per year. The annual average of daily mean air temperatures increased by 0.0544 °C per year. The rise of the annual average of daily minimum air temperature was the lowest, namely by 0.0374 °C per year. The air temperature rise was not the same in all periods of the year, and different increases were found in individual months. The daily mean air temperature rose significantly in the growing season (April–August). In all the other months except December, a statistically non-significant rise of daily mean air temperatureSymbol was recorded. From the ecological point of view, the different monthly increases are more important for the wetland ecosystem than the slow gradual rise of air temperature over the years. The air temperature rise recorded in the wetland studied was lower than that predicted by climatic models.