too close for comfort?

first kayaking session on the river and couldn't have better weather for it.
two swans were in residence by the school all last year but there was no sign of any signets - would they be 2 juveniles? do they pair up even if they are not ready for mating or would they be the same sex?
anyway, this year there is only one.
would it be one of last year's or is it a new one?
i know swans pair for life but do they return to the same nest? so many questions.
can anyone help?