SAND HARBOR, Nev. — Just after dawn on Sunday, with a white moon still visible over mountain-ringed Lake Tahoe, Fred Jackson maneuvered his small boat into clear water about 35 feet deep.


“Hard right — back up,” said his nephew, Justin Pulliam, standing on the edge of the boat and peering at a shadow at the bottom of the lake.


“You got it?” Mr. Jackson asked.


Soon his nephew was pulling up a trap containing a couple of dozen crayfish, the day’s first harvest. But more significant, it was the first act of commercial fishing in Lake Tahoe since the overexploitation and extinction of the Lahontan cutthroat trout led the authorities to ban all but recreational fishing here in the 1930s.


Last week, Nevada authorized the commercial trapping of crayfish after Mr. Jackson and a local scientist persuaded state authorities that it would be good business. And not only that, it would improve the famed, though vulnerable, water clarity of one of America’s greatest natural treasures.


Introduced to Lake Tahoe more than a century ago, the crayfish population has swelled to 280 million, up from 200 million just six years ago. The crustacean lives, eats and excretes in the lake’s shallow waters, contributing to algae growth, which clouds the water. Reducing their numbers would help keep the lake blue.


Commercial fishing’s resumption here seems to be riding a confluence of trends. Some environmentalists are exhorting people to combat the growing problem of harmful, invasive species by eating them. Crayfish harvesting is also in keeping with the more established locavore movement, which steers diners to locally grown food.


In Nevada, made up mostly of desert, the impending availability of a local seafood has made headlines in Reno, less than an hour’s drive northeast. Sierra Gold Seafood, a wholesaler that will sell Mr. Jackson’s crayfish, trucks in all its products from hundreds of miles away — everything except the Lake Tahoe crayfish now.


“This is it, man,” said Brandon Crowell, whose family owns Sierra Gold, adding that 40 restaurants and casinos in the Reno area had already put in orders.


At 250 square miles, Lake Tahoe is North America’s largest alpine lake, straddling the Nevada-California line. Commenting on the reflection of the surrounding snow-capped mountains on the lake’s “still surface,” Mark Twain wrote that “it must surely be the fairest picture the whole world affords.” But overuse and overdevelopment led to the rapid degradation of its crystal blue water in the 1970s and ’80s, a problem highlighted by President Bill Clinton during a summit meeting on environmental issues held here in 1997.


Since 2000, perhaps because of efforts to control runoff from surrounding areas into the lake, the lake’s deep water quality has stopped declining, experts say. According to the Tahoe Research Environmental Center at the University of California, Davis, which has been measuring Lake Tahoe’s water clarity since 1968, it is now clear down to nearly 69 feet, compared with 67 feet in 2000. In 1968, it was clear down to 102 feet.


But in the most recent years, the clarity of the water near the shoreline has “gotten considerably worse,” said John Reuter, the center’s associate director. Besides crayfish, other newer invasive species found in shallower waters, including Asian clams and Eurasian watermilfoil, an aquatic weed, are causing the clarity to deteriorate.


The League to Save Lake Tahoe, a 55-year-old private organization that engages in conservation activities, including sending volunteers to uproot Eurasian watermilfoil, said the new rules guiding crayfish harvesting are strict enough to protect the lake’s environment and recreational use.


“There is the ability to actually eradicate that species from the lake,” said Darcie Goodman-Collins, the group’s executive director.


Kristi Boosman, a spokeswoman for the Tahoe Regional Planning Agency, the bistate board that oversees the lake, said that eradication was “an unrealistic expectation” but hoped that harvesting would put a dent in the current population. (California is taking a “wait-and-see approach” toward commercial harvesting on its side of the lake, Ms. Boosman said.)


Ms. Boosman predicted more people would apply for crayfish permits if “Mr. Jackson is successful,” adding, “frankly, there are plenty of crayfish to go around.”