After more than forty years of construction, Mayor Bloomberg announced the official completion of the Manhattan stretch of Water Tunnel No. 3, a 13-mile-long tunnel that runs from Hillview Reservoir in Yonkers, south through the Bronx, and into Manhattan, eventually heading on through Roosevelt Island and into Astoria, Queens. Photographer Tod Seelie ventured down into one of the secret Main Valve Chambers 200 feet below the street for an illegal party press conference today, and resurfaced with this sweet infrastructure porn.

$4.7 billion well-spent! The city maintains it's crucial to have a third water tunnel in case the other two fail or need maintenance, and the massive project—which was first proposed in 1954—provides "crucial infrastructure redundancy," enabling Water Tunnel No. 1 to be taken offline and inspected. THAT tunnel has been carrying water to NYC from upstate reservoirs since 1917! Tunnel No. 2 has been in continuous service since 1936. By the way, here are some more heavy tunnel facts:

Tunnel No. 3 is lined with nearly 3 million cubic feet of concrete.

The new tunnel has claimed the lives of over 24 people in its construction.

The water tunnels sit roughly 500 feet below street level and vary in diameter between 10-24 feet.

82 million cubic feet of soil and rock has been excavated for Tunnel No. 3 so far—enough to fill Madison Square Garden more than 200 times.

The Bloomberg administration dedicated $2.7 billion towards the construction of Water Tunnel No. 3, more than the five previous Mayoral Administrations combined.

"If there was ever a major failure of water Tunnel No. 1, the potential for public health and safety consequences in Manhattan could have been really grim," the mayor said today. The portion of the tunnel activated by Mayor Bloomberg this afternoon is eight miles long, and since it's redundant, you won't notice it at all! (If you want to watch him turn it on now, here's video.)

The Brooklyn and Queens portion of Tunnel No. 3's Stage 2 is now the only segment that remains unfinished. Although most of the construction work, including the tunnel's drilling itself, has been completed, finishing of the network of smaller shafts that will bring water to mains near street level is expected to take until 2021.

In other breaking water news, the Bloomberg administration also recently completed the $1.5 billion Catskill/Delaware Ultraviolet Disinfection Facility, announcing that "ultraviolet light is a relatively new and revolutionary method for treating drinking water and will provide an added layer of protection against pathogens and other harmful microorganisms for the drinking water consumed by 9 million New Yorkers, including a million residents in upstate counties." And later this year, testing and startup will begin on the $3.2 billion Croton Water Filtration Plant in the Bronx.

Reporting by Scott Heins