I do laps at the pool quite often and when I do front crawl I breathe out with my face in the water.
I tried to do the same at a lake (it was quite warm actually but choppy conditions) but found it quite a bit harder to force air out of my mouth and nearly impossible to breathe out of my nose (which I prefer in the pool).
Is there anything about open water that would make this harder? Or was it psychological?
I didn't notice myself feeling tense (I was close to shore) - but I wondered if small currents from the chop, relative to a pool made the difference?