Editor's note: The following blog entry is based on experiences from Smarter Travel's company trip to Cancun, which took place from January 11 through 15.
I was surprised by just how rough the Caribbean was in Cancun's hotel zone, at least around kilometer 16 of Blvd. Kukulkán. The waves were big and from the safety of the sand I watched as determined swimmers got smacked around by the surf.
I'm not sure how typical the rough waters are for early winter, but less-than-ideal swimming conditions can't be that unusual, because there's a flag system in place along the beaches that rate the swimming conditions. I just did research, and though websites differ a bit on the number of flag colors, all follow the logical progression. White or green flags signify good swimming, yellow encourages caution, and red or black flags strongly discourage swimming.
While I was there, it was all red flags, but some people were still in the water. Everyone stayed close to shore though, and a lifeguard kept watch and moved people away from the most dangerous areas. A short ferry ride away on Isla Mujeres, however, the beaches near town offered calm waters and enjoyable swimming.