STATELINE, Nev. (AP) — The extraordinary efforts put into healing Lake Tahoe in recent decades show it's possible to preserve the country's greatest natural treasures for future generations, President Barack Obama said Wednesday.
Obama spoke at an annual summit dedicated to the alpine lake that Mark Twain called the world's "fairest picture" and renowned naturalist John Muir tried to designate a national park.
Democratic Sen. Harry Reid of Nevada launched the summit 20 years ago to draw attention to reductions in Lake Tahoe's famed clarity. President Bill Clinton spoke at the first one in 1997.
Here's a closer look at the popular water body that straddles the California-Nevada border:
— If emptied, Lake Tahoe would cover the entire state of California in 14 inches of water.
— The lake's 191-square-mile surface is three times larger than the District of Columbia.
— At 1,640 feet, Lake Tahoe is the world's 10th-deepest lake. The top of the Empire State Building would remain submerged if placed upright in it.
— The 330 million gallons of water that evaporate from the lake every day would fill 5,000 Olympic-sized swimming pools.
Lake Tahoe's loss of clarity has been fueled by housing construction, soil erosion, storm-water runoff, air pollution, automobiles and invasive aquatic species.
Its pristine conditions first were disturbed by 19th century cattle grazing, then logging to build Comstock-era mines and rebuild San Francisco after the 1906 earthquake.
In the decade surrounding the 1960 Winter Olympics at Squaw Valley, yearly visitation grew from 30,000 to 150,000. Today, the 3 million annual visitors to Tahoe's casinos, ski resorts, campgrounds and marinas drive a $5 billion local economy that would be jeopardized if further loss of clarity turns the lake a murky green.
"Keep Tahoe Blue." The phrase coined by the League to Save Lake Tahoe in 1965 has been printed on more than 1 million bumper stickers.
Underwater visibility stretched to a depth of 105 feet in 1968 when scientists first measured it by lowering a white, dinner-plate-sized disk into the water until it disappeared.
Clarity worsened by 30 percent over the next three decades — about a foot a year — falling to a record-poor 64 feet in 1997.
The rate of the loss of clarity has since slowed, registering 73 feet last year. The long-term goal is to get back to 100 feet, with a short-term goal of 78 feet by 2026, sustained for five years.
Nearly $2 billion has been spent on 400-plus restoration projects since the 1997 summit.
Congress approved a measure in 2003 allowing the sale of federal lands in Nevada to finance an initial $300 million investment at the lake over 10 years to be matched by private entities and state and local governments.
So far, the U.S. has spent $635 million, California $759 million, Nevada $124 million, local governments $99 million, and private groups $339 million. About $650 million of that was devoted to managing storm-water runoff that carries sediment into the lake.
Reid, who is retiring this year, hopes to generate support for future spending at the lake.
More than 700 miles of roads have been improved. A new public transit center opened in Tahoe City, California, in 2012, with additional bus routes, bike paths and walking trails to encourage reductions in traffic.
Certain types of jet skis that discharged fuel into the lake were banned, and mandatory boat inspections were imposed to curb invasive species.
More than 3,000 land parcels have been made off-limits to development. And emphasis has been placed on restoring wetlands that filter out pollutants and improving conditions of streams that empty into the lake.
Since 2009, Congress has been considering spending another $400 million at the lake over 10 years.
Meanwhile, scientists have identified a new threat: climate change. The lake's temperature has risen faster over the past four years than any time on record.
That appears to be contributing to changes in Lake Tahoe's internal physics, experts say. The lake's "mixing depth" last year — an important measurement of the intermingling of varying water depths — was the shallowest ever recorded.