SOUTH LAKE TAHOE, Calif. » Deep in the Sierra Nevada, 39 trillion gallons of crystalline water straddles the border between California and Nevada.

That water, Lake Tahoe, can be as smooth as glass, but the politics of land-use planning along the lake’s 72-mile shoreline are some of the most contentious and muddled in the country.

Lawmakers from the two states tend to have very different ideas about how to manage development around the lake, to say nothing of the 50-plus federal, state and local agencies with jurisdiction in the basin.

But last month, after nearly a decade of wrangling, the Tahoe Regional Planning Agency, the bistate agency that regulates development, approved a new plan that will guide building there.

"The infrastructure around the lake was built in the 1950s and ’60s, and it’s failing the communities and it’s failing the lake," said Todd Ferrara, deputy secretary of the California Natural Resources Agency. "California and Nevada have this shared treasure, and the stakes are too high not to work together to protect it."

The new regional plan encourages ripping down and rebuilding the area’s aging infrastructure, removing buildings from environmentally sensitive areas near marshes, streams and rivers, and constructing denser urban centers. It also streamlines the permit process for construction projects in the basin, which gets 3 million visitors a year.

For many of the basin’s 55,000 full-time residents, the fact that the agency’s governing board — made up of seven Nevadans and seven Californians — reached consensus came as a great relief.

"We’re very happy that a plan has finally been passed, because without concrete regulations, nobody wins and the lake suffers," said Darcie Goodman Collins, executive director of the League to Save Lake Tahoe, an environmental advocacy group.

While the plan has broad support on both sides of the state line, some environmental groups say it will result in taller buildings and denser development, which could ultimately harm the ecosystem of the lake.

"This new plan is a plan for improving the tourist economy, not a plan for improving the environment," said Laurel Ames, conservation co-chairwoman for the Tahoe Area Sierra Club, which is considering a lawsuit to halt it before it is implemented on Feb. 11.

But policymakers counter that replacing aging infrastructure would be a major step toward restoring the lake’s ecosystem and quintessential clarity.

"The idea is to get rid of this strip development that causes sediment to run off into the lake and rebuild," said Lew Feldman, a lawyer who represents developers in the area.

Beginning in the 1950s, developers hurriedly built in preparation for the 1960 Winter Olympics in Squaw Valley, Calif., and to support the burgeoning gambling industry on the Nevada side.

In just a few decades, whole sections of shoreline were rapidly transformed from stands of Ponderosa pine trees and willow-filled marshes into a kind of continuous strip of low-slung motels, casinos and budget eateries.

By the late 1960s, sewage was leaking into the lake, resulting in the growth of microscopic algae that clouded the lucent waters.

"Every little pebble was distinct, every speckled trout, every hand’s-breadth of sand," Mark Twain wrote of his unimpeded glimpse into Lake Tahoe’s depths in "Roughing It."

When scientists first began testing the lake’s clarity, in 1968, they could see down more than 102 feet into the water. By 2011, the most recent year with complete data, visibility was 69 feet and the summer clarity was the second worst on record.

To control the runaway development in the Lake Tahoe basin, Congress approved a bistate compact between Nevada and California in 1969, creating the Tahoe Regional Planning Agency.

"The focus is on water quality restoration," said Joanne Marchetta, the planning agency’s executive director. "The lake is the canary in the coal mine: If the lake is healthy, the surrounding environment and economies can be healthy."

The agency’s last regional plan, implemented in 1987, capped development and established standards for environmental quality in the basin.

"The bistate compact was created in an effort to strangle the uncontrolled growth that was undeniably polluting the lake, and it succeeded," said Ross Miller, Nevada’s secretary of state.

In fact, the compact restricted growth so rapidly it had the effect of freezing the lakeside communities in time. Much of the infrastructure still looks like it did when Elvis Presley spent summers there playing at the Nevada casinos in the early 1970s.

Other economic forces also hampered development. Beginning in the 1990s, the growth of Native American gambling in California sent Nevada’s casinos into a tailspin of lost revenue and empty hotel rooms.

By 2011, Nevada lawmakers became so frustrated with the agency’s strict development regulations that they passed legislation to withdraw from the compact in 2015 if a new regional plan was not approved.

"It is time for Nevada to stand alone in serving Nevadans and the valuable natural resource Lake Tahoe," state Sen. John Jay Lee, who sponsored the bill, said at the time.

Since the agency approved the new plan on Dec. 12, some Nevada lawmakers, including Miller, say that as long as the plan does not stall in the courts, they will rescind the bill and recommit to bistate management.

"The different states and stakeholders all come with different perspectives," Marchetta said. "But they share a passion for the lake and a desire to preserve it."

© 2013 The New York Times Company