I've seen estimates of the lifespan of the Hoover Dam on the order of 10,000 years. If you left it alone some exciting things would probably happen because it's

I've seen estimates of the lifespan of the Hoover Dam on the order of 10,000 years. If you left it alone some exciting things would probably happen because it's not all just concrete, there's turbines and ducts and so on, but the concrete structure will last a long time.