I read an article sometime back which gave a lot of clarity to what seems very related to electrocution in water. I am sorry, but I do not recall where I read it so I can neither quote from it or reference it.
It was about GFCI's and boat dock wiring and the dangers of electrocution surrounding that.
As you all well know, electricity takes the path of least resistance. When that path passes the heart it can easily cause death by putting the heart into arrhythmia, where the heart goes out of sync. It takes a very minute amount of electricity passing through the heart to cause this.
The salt water at seaside docks conducts electricity better than the human body, therefor the electricity passes around it. In lake water the human body conducts better than the water so if the person is in the path the electricity passes through the person and is very lethal.
As to the flood waters, they are usually very muddy, dirty, with many electrolytes in it. I would surmise that saves many lives.
In Dumas Texas in 1963 two girls were electrocuted on the lawn. A radio was plugged into an extension cord, and a sprinkler was on. One girl was getting electrocuted, the other came to help and also succumbed to it. I wondered about that for years, being as they started out on their feet, the electricity had to of taken a path through one foot, passed through the heart and back to the ground on the other foot. Reading the article about fresh water and the path of least resistance kinda cleared that up for me.
Just my thoughts on this matter.