Would you consider the meanders to be more significant if a boundary is defined to run along the main channel without qualification? This isn’t necessarily the case everywhere a boundary runs along a waterway, but it would probably be more common for more local boundaries.
Yes, I’m using QGIS 3.34 and it has the NADCON5 files included…
It’s important to use the “Reproject Layer” processing tool (under Vector general in the Processing Toolbox) instead of just setting the CRS for the layer or project. “Uses NADCON5…” will appear under “Remarks” under “Advanced Parameters” in the tool. It works well except for step 2 in the sequence on the OSM Wiki page. In QGIS, the description for the recommended transform NAD83(HARN) to NAD83(FBN) (3) - DERIVED_FROM(EPSG):8865, says “Guam”, etc. and any results do not appear at all on the QGIS base map. I used (1) - DERIVED FROM(EPSG):8861 instead. It’s described as "United States (USA) - CONUS onshore… " and seems to be the appropriate choice.
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You are right, and I fixed the page. NAD83(HARN) to NAD83(FBN) (1) - EPSG:8861 not NAD83(HARN) to NAD83(FBN) (3) - EPSG:8865
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Oh, I need to upgrade, lol. Thanks. 
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When the waterway main channel is used for a administrative boundary, I like including the waterway way as a member in the administrative boundary relation rather than double-mapping what is essentially the same feature! Realign the waterway with updated imagery, realign the admin boundary at the same time. Bonus points if you move the former alignment to OHM!!!
Moving on to Wyoming. The North Platte River extends upstream well beyond Glendo Reservoir westward and then south into Colorado. Nearly all of that stretch is missing from OHM. I have started importing that and including riverbanks and reservoirs. I’m also adding tributaries but restricting those to named waterways. Even with that restriction, I think the detail may be too much for a first pass (at least in terms of time and effort).
The NHD in this area seems to align much more closely with older topographic maps (1950-1960) than with the Bing imagery. Most of that difference seems to be due to meandering streams. Is there any way to determine the age of the imagery?
In iD, open the Background panel on the right and check the Show Background Details checkbox. A little black box will appear in the lower-right corner with a date range for the imagery you’re looking at. This also works for the Esri World Imagery layer.
Thank you, Minh; that date information helps. I;'m now adding the North Platte River between Guernsey and Casper, Wyoming. Proceeding slowly, in part because I’m getting sidetracked with some of the local history. E.g. the difference in the La Prele reservoir geometry between the NHD import and Bing. imagery is due to lowering the lake level behind a 1909-vintage dam in 2019 for safety reasons. OpenHistoricalMap
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The North Platte River from Guernsey, WY upstream to its headwaters near Walden, Colorado is now on the map. I combined existing entries from other mappers with NHD imports and some manual image tracing. To help with time placement (for anyone interested), I have started including the NHD:FDate field which is the last edit date for an object. These are typically 10-15 or so years old, but much of the data aligns nicely with 1950s vintage topographic maps.
For now and for most uses, I would consider these as a close-enough approximation of the current water geometry. But local mappers may want to edit these or even map changes over time. E.g. comparing NHD data with the much more recent Bing imagery can reveal some key changes in stream geometry.
Still to do: add some tributaries and check relations before moving on…
Where possible, I have added the pre-dam river channels to reservoirs. Data showing these is available for some of the major reservoirs along the North Platte River (Pathfinder, Grey Reef and Glendo). Others have been “straight-lined” through. A series of maps from 1903 shows the streams and area to be inundated behind the dam, completed in 1909. These were warped and rectified as best as I could for the pre-dam Sweetwater and North Platte river channels. See: OpenHistoricalMap