Today, aquatic sports and activities rank high among Americans’ favorite ways to recreate. Not only do we love to splash and play on a hot summer day, we’re also more keen than ever to support professional swimmers during big events like the Olympics. Still, a surprising number of folks across the country don’t know how to swim. We’ve gathered some striking stats on the way swimming as sport and recreation has changed over the years — the numbers might surprise you.

660,000: Gallons of water in an Olympic-size swimming pool.

25-27: Hours the American Red Cross requires for a certification in lifeguarding.

309,000: Number of public swimming pools in the United States as of 2004.

91 million: Number of people over the age of 16 who swim in oceans, lakes and rivers each year in the United States.

4: Where swimming ranks on the list of most popular recreational activities in the United States.

301 million: Number of visits by persons over the age of six to a swimming facility during 2009.

2,500: Number of private in-ground pools in the United States in 1950.

5.2 million: Number of private in-ground pools in the United States in 2009. 

65: Percent of Americans who do not know how to swim.

650: Calories burned during one hour of constant swimming.

1896: The year swimming became an Olympic event.

Sources: http://water.epa.gov, www.redcross.org, www.cdc.gov, www.huffingtonpost.com and www.swimmingpool.com.