Stream-bed temperature profiles were used to examine hyporheic water patterns beneath Chara hummocks in a northern Michigan (U.S.A.) stream. Hummocks were found to alter expected hyporheic temperature patterns significantly, causing apparent upwellings of deeper, colder waters into the hummock. The magnitude of the temperature pattern alterations was proportional to the size of the hummock, and hummocks were often situated in areas of the stream where cooler hyporheic water was closest to the stream-bed surface. Upwelling and downwelling patterns caused by hummocks conformed to the literature on hyporheic flow alterations imposed by inanimate objects on the stream-bed surface. Hyporheic water upwellings may be of benefit to Chara by exposing the anchorage system to higher nutrient or ion levels existing in interstitial water.