Below is a picture of the Pacific Ocean temperatures relative to average. Warmer and cooler pockets are easily visible. The El Nino is the band of warmer colors in the middle along the equator.
Consider that the length of Lake Erie is approximately 240 miles. The distance across the main ENSO region in the yellow box below where the core of the warmth is located is roughly 5000 miles. The depth of this warmth is roughly 100 meters or slightly more than 300 feet.
The area boxed in yellow is roughly equivalent to 75% of the contiguous United States.
Performing a quick volume calculation (area times depth), we come up a HUGE volume of relative warm water in the El Nino region using these parameters:
The VOLUME water in the equatorial Pacific Ocean where water temps are running at least 3 degrees Celsius (~5 deg Fahrenheit) above normal is more than 25 TIMES GREATER than volume of ALL the Great Lakes! WOW!