On August 7, 2003, at 1415 mountain daylight time, a Schempp-Hirth Ventus B/16.6 glider, N25RN, was substantially damaged during a precautionary landing in Gross Reservoir, near Boulder, Colorado. The commercial certificated flight instructor, the sole occupant on board, was not injured. Visual meteorological conditions prevailed. No flight plan had been filed for the cross-country flight being operated under the provisions of Title 14 CFR Part 91. The glider departed Boulder, Colorado, at 1130. According to the pilot, he was soaring 8 miles northeast of Mount Evans, when he noted the formation of thunderstorms and rain showers along his route of flight. He elected to return to Boulder. During his return flight, thunderstorms developed along the foothills, just west of Boulder. Due to the inadequate lift to sustain flight and with unsuitable terrain between his position and Boulder, the pilot decided to ditch the glider in Gross Reservoir. The pilot reported that he positioned the glider to land into the wind, a "west/northwest direction[,] parallel to the shore." During the impact with the water, the glider canopy was destroyed and the wings were separated from the fuselage at mid-span.