We were forbidden from taking boats across the lake after that - not that I ever did. These two were from a different mission, but were there to pick up someone's Fe de Edad (birth certificate) so that a couple could get married before getting baptized. That was pretty common at the time - need to get couples who had been together for years officially married before they could get baptized.

I was never assigned to the area closely enough to hear the stories that you are referring to - but I know that it was a big enough lake and was known for sudden storms coming up that would lead to large waves. And it wasn't uncommon for the little boats to capsize there.

Here's an article on the missionaries: