[Tagging] Maritime=yes for marine river estuaries?

[Joseph Eisenberg]

I discovered that maritime=yes has been used about 100 to 150 times to
tag areas of river estuaries that should be considered part of the
marine environment.

These parts of rivers are sometimes mapped outside of the coastline,
but in some places the local community feels strongly that the water
body should be tagged as a river. The most infamous example is the Rio
de la Plata between Uruguay and Argentina. This has been done since at
least 2015, and has been used by some database users (eg
http://openstreetmapdata.com/data/generalized-coastlines - although
this is moving soon).

The tag was approved for use on administrative boundaries as a way to
specify that the boundary way is outside of the coastline, and has
been used about 9000 times in this way (most admin_level=2 and many
other administrative boundaries are tagged when they are in the sea),
which is quite helpful for rendering marine boundaries differently.

But I wonder if it wouldn't be better to make a different tag for the
usage on marine rivers and estuaries? This would make it possible to
keep the tag marine=yes defined for use on administrative boundaries
only.

I had previously thought that "river=estuary" could work to tag areas
of water that are also tagged waterway=riverbank or natural=water +
water=river but which are transitional to the marine environment.
Alternatives could be "river=marine" or "river=maritime".

There is also the popular tag "tidal=yes" but some parts of the
coastline have very small tides, so not all marine estuaries are
clearly tidal.