There's a difference between legally navigable and practically navigable. The Dee has a public right of navigation and therefore is tagged as boat=yes in OpenSt

There's a difference between legally navigable and practically navigable. The Dee has a public right of navigation and therefore is tagged as boat=yes in OpenStreetMap. That's not to make any judgement as to whether or not you can get your boat through the Chester weirgate! The Mersey ought to be tagged with boat=yes, though. I'm now wondering about Walton Lock which I think still has a right of navigation though is very definitely impassable...