Low water levels in Lake Tahoe have caused one cruise company to modify the path of a ship while leaving another out of commission altogether.

As of two weeks ago, the M.S. Dixie II at Lake Tahoe Cruises can no longer enter Emerald Bay without risking damage to its propeller, said Teri Sweeney, director of sales and marketing for Aramark Lake Tahoe.

While the Dixie is still offering cruises without going into Emerald Bay, the Tahoe Queen has stopped running cruises completely.

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Sweeney said low lake levels are to blame.

“We were able to react and come up with new plans around here,” she said, “but it’s constant change when you live in an alpine environment.”

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As lake levels continue to drop, the region faces a number of challenges that could arise as soon as summer, Federal Water Master Chad Blanchard said. Many of them would come about if water levels drop below the lake’s natural rim.

If that happens, recreation on Lake Tahoe and the Truckee River — the only river Tahoe releases water into — could be significantly impacted, he said. Some water sports, such as river rafting, could be halted.

“All we can do is wait and hope things turn around,” Blanchard said.

As of Tuesday, the surface of Lake Tahoe was at 6,223.56 feet above sea level, according to U.S. Geological Survey measurements at Tahoe City — slightly above its 6,223-foot natural rim.

While lake levels are above the rim now, they won’t be for long if the area continues to receive little precipitation.

“If we stay dry,” Blanchard said, “we will go below the rim this summer.”

It’s not uncommon for the lake to fall below the rim, he said, and it’s still a ways off from reaching its record low in 1992, when the lake dropped to 6,220.26 feet.

Several factors contribute to the water loss, but the biggest is evaporation, Blanchard said, which accounts for about 10 times more water loss than outgoing water flow. Unfortunately, higher temperatures and drier climate aren’t slowing that process, he said.

The lake just came out of its driest year on record, Blanchard said.

It also experienced its warmest temperatures on record in 2012, said Julie Regan, chief of external affairs at Tahoe Regional Planning Agency, at a weather conference last Thursday in Stateline.

“We’re all very concerned about this drought and what it’s doing to the aquifer and particularly to the water supply that people downstream rely on from the Sierra Nevada,” Regan said.

One drop of water entering Lake Tahoe takes 600 years to make its way out, she said. Yet, water levels are still falling.

Precipitation this winter could help turn things around, but the dry weather isn’t a good sign, Blanchard said.

“When we’ve started out this dry in the past,” he said, “we have not had a big year.”