However, under the pristine blue-turquoise water lays evidence for a supervolcano that is still active. There are features on the bottom of the lake ranging from hydrothermal explosion craters, siliceous spires, hundreds of hydrothermal vents, active steam fissures, and gas pockets.
One of the oddities that sparked the search for these features sits on the floor of Bridge Bay Marina. This large silica spire that was found in 1996 looked to scientists to be similar to the spire-like hydrothermal structures that are found in deep ocean thermal areas like the mid-Atlantic ridge. Sample pieces from the spire were taken as well as a smaller spire that was found along the floor. After a CAT scan, the spire showed that it was made up of a layered structure with porous conduits for hydrothermal circulation. These spires were formed when ascending hydrothermal vent fluids left the lake bottom. The outer shell of the spire was precipitated due to the hot water mixing with the ambient lake water and cooling by dilution. The inner section was made up of small channels that make a porous silica center.
Not only do hydrothermal features reside in the lake but an invasive trout species called Lake Trout do as well. These fish are estimated to have been introduced to Yellowstone Lake sometime in the mid 1970’s as a stock fish to increase the lake’s fishing for anglers. No one could have predicted the negative effect that the Lake trout had on the native species of Cutthroat trout. The Lake trout grew larger and lived deeper than the Cutthroat. They started using the Cutthroat as a food source, decimating the populations within Yellowstone Lake. Because the Lake trout lived deep within the lake, predators such as bears and fishing birds couldn’t reach them as a food source. Their original food source, the Cutthroat, was now being eaten by almost exclusively by the Lake trout.
In the mid-nineties, the park started hiring commercial gill-netting companies to catch Lake trout deep at the bottom of the lake. With continued aggressive Lake trout control efforts, park biologists expect the Cutthroat population to rebound, although they also admit that Lake trout will probably never be removed completely from the lake.
For more info about Yellowstone Lake, check out the park website at http://www.nps.gov/yell/