Seasonal trends of surface temperature in the Narragansett Bay estuary were derived from a composite of 14 thermal infra-red satellite images (Landsat TM Band 6) with a spatial resolution of 120 meters. Relationships among thermal properties and physical characteristics were identified through a comparison of the seasonal temperature patterns of 12 regions within the bay. Correlations among the seasonal temperature signals of these regions were used as a basis for categorizing the estuary in terms of its thermal behavior. The lower estuary was characteristically cooler than the bay average during the summer and warmer during the winter due to the influence of oceanic water, which always has a more moderate temperature than the estuary. The thermal characteristics of lower estuarine regions were most dependent upon circulation patterns. The upper estuary was warmer than the bay average during the summer and cooler during the winter because it gains and loses heat more quickly and extensively than the ocean due to its shallowness. Depth is the most important factor in determining the magnitude of seasonal temperature variation in the upper estuary. Although the behavior of Mount Hope Bay was significantly correlated with the other upper estuarine regions, the bay did not experience autumn cooling, which is characteristic of upper estuarine waters. From late summer through autumn, the average temperature difference between Mount Hope Bay and Upper Narragansett Bay was 0.8°C, which can be attributed to warming from the thermal effluent of the Brayton Point Power Station in Mount Hope Bay. An unsupervised (statistical) classification of temperature as a function of season revealed the natural boundaries between areas with different seasonal temperature signals, and statistically identified Mount Hope Bay as a unique area in the upper estuary which had anomalously high temperatures throughout the year. Among the scenes included in the unsupervised analysis, Mount Hope Bay was on average 0.8°C warmer than the rest of the upper estuary.