Every three weeks, Metro sends a crew into a massive, dark tunnel about 13 stories below the Red Line’s Medical Center stop to scoop out buckets of water and mud that leak onto the tracks.

Metro also uses aluminum tents that look like Reynolds Wrap foil to line that same portion of the tunnel walls and divert the gunk away from critical systems and into drains. Last year alone, the transit agency spent $4.3 million trying to pump water out of a three-mile stretch on the Red Line that runs between the Friendship Heights and Medical Center stations.

But the myriad fixes Metro officials have tried over the past decade to try to stop the leaks have had the same effect as applying a plastic bandage to a gunshot wound.

The leaks have become a strain on manpower, time and money.

Water has interfered with the 750 volts along the third rail that powers trains. In the past year, more than a third of the incidents involving smoking insulators on the system have been linked to water leaks along part of the Red Line. A smoking insulator on a track often leads to delays for riders.

The water-logged tunnel between the Red Line’s Medical Center and Friendship Heights stations has forced Metro’s leak-pluggers and water mitigators into a resource-sucking game of Whac-A-Mole. Here’s why the tunnel is so wet:

Now, the agency is looking for a long-term — and potentially more costly — fix, as it says it needs to upgrade the system to deal with running more and longer trains.

“We’re fighting a daily battle,” said Rob Troup, Metro’s deputy general manager of operations. “We’ve patched holes and plugged holes.”

“It is a maintainability and reliability issue,” Troup said.

One of the solutions could involve shutting down parts of the Red Line between Friendship Heights and Medical Center for several weeks, according to Metro. The mere mention recently of a possible shutdown set off a flurry of complaints from riders, local officials and business owners.

Some business owners wondered how employees would get to work and talked of lost revenue if customers couldn’t patronize their restaurants and stores. Transportation experts said some of the roughly 40,000 weekday commuters who use that portion of the Red Line might permanently abandon the transit system and take to their cars.

But finding a longer-term fix to the leaks may mean Metro has no choice but to close a portion of the busiest rail line, according to experts.

Metro officials caution that they are four to five months from making a decision about how to make the fix, and they do not definitively know whether a shutdown of a portion of the Red Line would be needed. One remedy would involve shutting down parts of the line for four or five back-to-back weekends.

The solution that may have the greatest chance of success would require installing a much-needed protective waterproof liner along the tunnel walls, experts said. Metro said it is work that is too complicated to do in off-hours or on weekends and may be the best — and only feasible — solution to fix the leaks. Critical switches in the Medical Center area had been so regularly covered with mud that until two years ago they weren’t used. Now they are cleaned more often to keep trains running if they have to share a track.

Ten years ago, when Metro officials considered relining a portion of the tunnel walls near Medical Center, it was estimated that it would take more than a year to complete one mile, at a cost of $9 million per mile. It was then deemed too disruptive and too costly.

Metro also worked with the U.S. Geological Survey to study the leaky area near Medical Center. Their 2004 study said that the leakage would “eventually reduce the life span of the structure and rail system.” A solution: Drill wells in the Medical Center area and pump out the water that flows onto the track bed. But experts warned that “it could be a very costly” fix.

Allen M. Shapiro, a research hydrologist at the U.S. Geological Survey who has looked at Metro’s leaks, compared it to a leaky roof on a house.

“You can set up buckets to catch the water and do some patching of the roof and put off replacing the roof,” he said. But “it will eventually become an issue of cost and inconvenience of continual maintenance versus the cost of replacing the roof.”

The agency has hired the Pennsylvania-based engineering firm Gannett Fleming to help find a long-term fix to the leaks, and it plans to get “peer reviews” of the solutions from subway experts in Chicago, New York and London.

The effort to fix the leaks comes as Metro is trying to rebuild a 37-year-old transit system that current management says has not been well-maintained over the past several decades. Escalators and elevators routinely break, leaving commuters to climb long staircases at stations. There are near-daily hiccups that include cracked rails on tracks, signal problems, downed track circuits, malfunctioning doors on trains and a recent derailment that caused passengers delays.

Some watchdogs have questioned whether Metro’s management has done enough to deal with the water problems.

“If there had been an option earlier that was less disruptive and they failed to pursue it and now we’re at a place where we’re having to consider shutting down parts of the busiest rail lines on the Metro system, that is poor management,” said Roger Berliner, a member of the Montgomery County Council who has written to Metro leaders urging them to think carefully and coordinate with local governments on any possible Red Line shutdown. “There is no sugarcoating that.”

The subway is one of the deepest in the world, with tunnels and underground stations at or below the water table. One of the most troubled areas is a nine-mile portion of the Red Line that goes from Farragut North to Medical Center, according to engineering experts. Because of the geology of that area, which runs in part beneath Rock Creek, and because that portion of Metro was built in the 1980s when engineering practices were not as advanced, there is no protective waterproof liner in the tunnel. That has allowed water to seep in through cracks. The water problem is worst between Friendship Heights and Medical Center.

Water is no friend of a rail system. It rusts and corrodes the rails on the track, fasteners, the power system, electrical components and the steel girders that support fire pipes, communications cables and power lines.

“It’s taking its toll,” said Tom Robinson, Metro’s deputy chief engineer. “It has accelerated the wear.”

The leaks also have allowed mineral deposits to clog drains. Water and humidity have caused the wearing down of insulators to the point where there has been interference in the flow of electricity from the 750-volt third rail to the trains.

Rodrigo Bitar, assistant general manager for Metro’s infrastructure and engineering services division, said, “We can’t be efficient if we have to keep putting resources there.”

If there is a shutdown of part of the Red Line, deadlines have to be met, said Mort Downey, a vice chairman of the Metro board of directors.

“I’d like to make sure they really know how to deliver it,” he said. “If we say it is two weeks, four weeks or six weeks of a shutdown, we need to stick to that. It shouldn’t be an open issue.”