There’s actually a pair of swans here, mating.
Followed up by both having a good preen.
One bird (the female?) then built a nest one one of the small islands holding a pier of the bridge. The limits of the perfunctory looking nest are marked by a child’s hat which has been dropped from the bridge and an empty drinks can.
Later, and the swan is now preening a few yards away from the nest.
The lone egg will probably still be warming in the hot afternoon sun. But the pair give many signs they may be inexperienced. The river only needs to rise a few inches to sweep away the nest.