Abbot's pond, a small body of freshwater up to 4 m deep, was thermally stratified on a seasonal basis during much of the period May 1966-April 1967, when detailed observations were made. The persistence of stratification is attributed to the absence of wind disturbance of the water column, the pond being sheltered by old established woodland. Changes in the distribution of temperature were related mainly to heat exchange between the water mass and the atmosphere. There was associated stratification of dissolved oxygen and of dissolved ions. The presence of intermediate and inverse thermal stratification, above 4° C, during autumn and winter, is attributed to transfer of heat, previously stored in the sediment, to bottom water made denser than overlying cooler water by of water surface/year. The energy input from litter into the Thames was a very low proportion of the population metabolism of fish, but the nitrogen input could have been an important element in the economy of the river.