The disposal of drums of sodium into Lake Lenore, an alkaline lake in the Grand Coulee area of eastern Washington State, in 1947 by the War Assets Administration.
[A]fter WWII, the US government found they had some extra sodium no one wanted, so they disposed of it.
In a lake. Full of water. And by the way, it was ten tons of pure sodium.
Safety and environmental impact disclaimer
Oh, and all that surplus WWII sodium? While that would destroy the ecology of a lake, in this case it was already a heavily alkaline lake with no fish in it. While I wouldn’t say this was a great thing to do, at least they thought to minimize the impact. But cripes: don’t try this at home.