I'm not going to get into the hows and whys, but all my bees ended up going for a swim. Unfortunately they can't swim!

There my bees were, all sitting at the bottom of some fairly deep water. Fortunately I was able to build a high enough diving board to retrieve them - after taking off my cape, of course.

Lesson learned: Don't build your bee hives over deep water, especially if there are mischievous fuling nearby.