We discuss the results of bottom temperature monitoring run in October through December 2005 in the deepwater basin of Lake Teletskoe at a lake depth of 320 m using an autonomous recorder. The obtained temperature patterns of water and sediments to a depth of ~1.4 m show sudden large changes. Bottom water temperature fluctuated between 2.9 and 4 °C, and the sediment geothermal gradient changed from –360 to +170 mK/m for the period of measurements. Water temperature became 0.6 °C warmer through November and suddenly switched to cooling after 5 December, and the drop reached 1.15 °C for the following 22 days. The change in water temperature caused the respective change in sediments, namely, gave rise to a positive geothermal gradient. Estimating the deep component of geothermal gradient (heat flow) with this climate noise requires a longer experiment of more than one year.