Before the dam was built, Colorado River temperatures ranged from over in the heat of summer to just above freezing in winter. Today, water released by Glen Canyon is a consistent throughout the year due to a thermal mass effect in Lake Powell. The water typically released from hundreds of feet below the lake surface through the penstocks is insulated from temperature fluctuations by the thick layer of water above it. Nikolai Ramsey of the Grand Canyon Trust describes the clearer, colder river as a "death zone for native fish", such as the endemic Colorado pikeminnow and humpback chub, which are adapted to survive in warm, silty water.