Ben, I've noticed the same.
The answer seems to be yes, yes, maybe and yes

Yes, it has something to do with polarization.
Yes, a pola filter could have something of a similar effect.
Water is not a perfect reflector, and it may be colour-dependent?
Yes, you could have been seeing things!

Like rainbows, this it one of the things you have to pass up on if you insist on wearing sunglasses at all times...