Green’s Dictionary of Slang

bullock’s liver n.

a river.

1905		Duke Tritton’s Letter n.p.: I came to a Bullock’s Liver where I reckoned I’d have a Lemon Squash and liven up a bit.
1960		J. Franklyn Dict. of Rhy. Sl. 44/2: bullock’s liver A river. Late 19 C., and very popular in the army during the 1914–18 war, but now seldom heard.
2002		Pete’s Aussie Sl. Home Page 🌐 bullock’s liver: a river.