How un-upgrade a wide river from a narrowboat canal?

[AP]

In the current server game, at the confluence of a narrow river with rapids with a wide river,  in upgrading the narrow river in order to allow barges past the rapids, I have inadvertently "upgraded" the confluence tile.

Therefore in a very long wide river, I have a single tile of narrowboat canal (5744,2093 in the server game).

I cannot work out how to fix this  - advice? Is it a bug?

I am surprised it let me over-write wide river with narrowboat canal, because it is a downgrade in terms of the vehicles which can pass.

It won't let me "demolish" the canal back to wide river. Nor can I "remove" the canal to get back to wide river.

Nor can I build a ship canal past the "obstruction" because it is at too high an altitude for that canal type to be permitted.

I fear this unnatural constriction of this important waterway may cause flooding upstream come spring...

[DrSuperGood]

I am guessing the placement logic does not factor in the ship size like it does with maximum speed.

As far as I am aware there is no fix. Like deleting a river, once it is done it is done permanently.

[AP]

Ok, that sounds like a bug to me. Thanks. Edit: reported.

[jamespetts]

As discussed elsewhere, allowing over-building of rivers with inferior canals was a bug, which has now been fixed. There is no ability to reverse canalising a river short of building a new river over the canalised tile (which requires being the public service player), as the tile does not remember that it used to be a river.