It can't be the result of the stage of the moon, since unless I'm grossly mistaken, no matter how much of the moon is or is not reflecting sunlight, the entire moon is still actually there exerting gravitational pull on the water.
But I'm a history major, so what do I know?
UPDATE: Long-time reader Jeff M. sent me this explanation:
Tides are symmetrical. The moon exerts them on the side of the planet it is on AND on its antipode, because what's actually happening is the gravitational stretching of the earth. At full moon, the sun is also in line with the tidal axis. The sun's additional gravity raises the tide level.
I started to write that it had to be the position of the sun, which the stage of the moon reflected rather than being the driving force, but figured my input would be as valuable as saying the engine makes the car go.
I did have Astronomy in my first term of college oh so many decades ago. But I was not much interested in it. I'm reasonably sure I never used the word "antipode" in a sentence that semester.
A week before the first test, I was among a large group who still did not have a text book. The professor was frustrated and went off about just what did we think we were going to do the night before the test if we didn't have the text?
I responded that I was just hoping for a clear sky. I got a laugh out of him, at least, and an end to the admonition as he shook his head and resumed teaching.
I did get a B, anyway. Thanks, Jeff.
