[JerseyHighlander]

Up until the early 2000’s the harbor masters would tell any ships with barnacle problems to move to the Gowanus Canal overnight. The water was so toxic it would kill the barnacles in under 8 hours. It’s not easy to kill barnacles...

I highly doubt there is any natural material or corrosive metal objects of historical importance that be be found inside the canal, though possibly there could be objects behind the breakwalls, though again, the chemicals probably got to them.

[Pharmboy]

Although I never knew that, I sure can—as an old Brooklyn boy—understand it.

[blam]

"Up until the early 2000’s the harbor masters would tell any ships with barnacle problems to move to the Gowanus Canal overnight. The water was so toxic it would kill the barnacles in under 8 hours. It’s not easy to kill barnacles..."

Whew. That's amazing.