Sorry if this is kind of gross, but what about bathroom during OW events?

So I've got several open water events this summer. The last time I did an open water event. it was a 5 mile swim, so 2.5-3 hours in the water. The question I have is...excuse me.. but what if I need to have a bowel movement during the swim? Or do you guys do something to avoid needing a bowel movement? IDK a laxative the day before to clean yourselves out? It was really distracting during my last event. 

Any suggestions would be appreciated..

Thanks.