See for instance zooborns.com, back in 2011
Recently, Houston Zoo keepers gave Baylor and Tupelo a big kiddie pool. Now that Baylor weighs more than 1100 pounds and Tupelo weighs more than 600 pounds, the small, inflatable pools do not last longer than 5 minutes without getting popped. The babies now get a family size pool which is 120 inches in length and holds both calves. It is a lot more durable.
What a scoop for the pool manufacturer: “This pool has been tested by elephants!” :-)