Could it be...

+ There was something in the water, like more weads or growth, that kept the
waves from building?

+ There was oil on the water. I've heard that even a thin layer of oil will
effect wave action.

+ That normally, but not this day, there is some wind that catches even
little waves and makes them a little more pronounced?

+ That normally, but not this day, there are lots of other waves from either
wind or boats that cause interference with all
the waves and make them all more pronounced?

Just guessing around.