Green’s Dictionary of Slang

pond, the n.

[deliberate understatement]

1. [late 18C+] (also the big pond, the fish-pond) the ocean esp. the Atlantic Ocean.

2. [1910s–20s] the English Channel.

3. [1960s] (US) the Pacific Ocean.

4. [2000s] (N.Z.) the Tasman Sea.

In phrases

big pond (n.)

[mid-19C+] (orig. US) the Atlantic Ocean.