New York ? Two hours north of New York City, a mile-long stream and a marsh the size of a football field have mysteriously formed along a country road. They are such a marvel that people come from miles around to drink the crystal-clear water, believing it is bubbling up from a hidden natural spring.

The truth is far less romantic: The water is coming from a cracked 70-year-old tunnel hundreds of feet below ground, scientists say.

The tunnel is leaking up to 36 million gallons a day as it carries drinking water from a reservoir to the big city. It is a strong warning sign of a larger problem around the country: The infrastructure that delivers water to the nation’s cities is badly aging and in need of repairs.

The Environmental Protection Agency says utilities will need to invest more than $277 billion over the next two decades on repairs and improvements to drinking water systems. Water industry engineers put the figure drastically higher, at about $480 billion.

Water utilities, largely managed by city governments, have never faced improvements of this magnitude before. And customers will have to bear the majority of the cost through rate increases, according to the American Water Works Association, an industry group.

Engineers say this is a crucial era for the nation’s water systems, especially in older cities like New York, where some pipes and tunnels were built in the 1800s and are now nearing the end of their life expectancies.

“Our generation hasn’t experienced anything like this. We weren’t around when the infrastructure was being built,” said Greg Kail, spokesman for the water industry group. “We didn’t pay for the pipes to be put in the ground, but we sure benefited from the improvements to public health that came from it.”

He said the situation has not reached crisis stage, but without a serious investment, “it can become a crisis. Each year the problem is put on the back burner, the price tag is going to go up.”