Lake Tahoe’s famously blue waters – which make it the clearest lake of its size in the United States – attract three million visitors to California and Nevada each year. But decades of development, and now climate change, threaten this national treasure. This QUEST half-hour documentary takes you behind the scenes with the scientists working to keep the lake pristine and protect it for generations to come.
But Lake Tahoe isn’t the only body of water that comes to mind when we think about America’s most treasured lakes. The Great Lakes, an interconnected set of five lakes which include lakes Erie, Superior, Huron, Michigan and Ontario, hold 18% of the water on the face of the Earth. Both Lake Tahoe and the Great Lakes face environmental challenges, but are differently equipped to handle them because of their particular characteristics.
Similarities between Lake Tahoe and the Great Lakes
Both the Great Lakes and Lake Tahoe provide potable water to surrounding populations, though at very different scales. The Great Lakes deliver 43 billion gallons per day, hundreds of times more than Lake Tahoe. Lake Michigan alone provides drinking water to 12 million residents. Around three quarters of the water taken from the Great Lakes is used to cool down power plants
Lake Tahoe and the Great Lakes are warming up, just like all lakes around the world. “We’ve had some summers where the surface temperature is very, very warm, compared to 20, 25 years ago,” said Brant Allen, of the University of California-Davis’ Tahoe Environmental Research Center. Although it’s nice for visitors, heat encourages the growth of microscopic algae that scatter the light off the lake’s surface and make it appear cloudy.
Up north, intense spring rains that washed fertilizer into Lake Erie, coupled with a warm summer, contributed to a 2011 algae bloom that covered the surface of the lake’s western basin with a bright green scum. “All of the factors that happened in 2011 are the types of factors that we expect to see more commonly in the future,” said Anna Michalak, a Great Lakes researcher at Stanford University.
Zebra mussels and quagga mussels have invaded the Great Lakes, damaging sport fisheries and clogging intake pipes with their hard shells, to the tune of $1 billion per year. The mussels have hitched rides out west on recreational boats. But so far they haven’t reached Lake Tahoe, and authorities there are fighting hard to keep them out by inspecting every boat before it goes into the water.
“At first, I thought the public would be very resistant to the idea of paying fees for boat inspections,” said Geoff Schladow, director of the University of California-Davis’ Tahoe Environmental Research Center. “But the more people I talk to, they’re very accepting of the need for it.” Lake Tahoe is already dealing with the invasive Asian clam, which produces algae mats that wash up on its beaches, and an aquatic plant called milfoil, which sticks to boats’ propellers.
Differences between Lake Tahoe and the Great Lakes
Lake Tahoe is the eleventh deepest lake in the world. Lake Erie is the tenth largest lake in the world. At its deepest point, Lake Tahoe plunges to 1,645 feet – which makes it deeper than the Empire State building is tall. And this depth helps the lake stay clear, since its 39 trillion gallons of water are able to dilute the tiny dirt particles and nitrogen and phosphorus that threaten its transparency. By contrast, Lake Erie’s deepest point is only about 200 feet deep. With less water to dilute the nutrients that algae feed off, Lake Erie is particularly vulnerable to algae blooms.
Lake Tahoe is fortunate in that its watershed is small and the soil around it is relatively nutrient-poor. The 63 rivers that feed Lake Tahoe travel through an area about the size of the lake itself. Most lakes have watersheds many times bigger, which give tributaries more of a chance to pick up pollutants as they flow towards the lake.
Lake Erie has suffered from a steady flow of phosphorus from agriculture, which has contributed to bad algae blooms. Corn is planted widely in the Plains – partly to produce ethanol for use as a biofuel – and requires a lot of fertilizer. “The national biofuels program is what’s pushing more corn production,” said Stanford scientist Anna Michalak.
To keep their watersheds from becoming sources of pollutants, authorities at Lake Tahoe and the Great Lakes have efforts underway to prevent dirt from running into nearby rivers (Tahoe), and reduce the amount of fertilizer used on crops (Great Lakes).