There is a canal that runs alongside the Loire, called the Canal Latéral la Loire, and it crosses the river Allier not far from Km0 on the Loire à Vélo trail, via an aqueduct.
The aqueduct is quite high, and gives spectacular views over the surrounding countryside, and down to the Allier below. You can walk along it; cyclists are asked to dismount, although not everyone did. At the western end there is a deep lock, the deepest I have seen, to take boats down to the next level.
I liked the decorative lions on the handrails along the aqueduct, and also the flower boxes on the beams of the lock gates. Nice touches, both of them.
The river below was glistening in the morning sun.