Hi
While using the Water polygons to decide whether some objects are within a certain distance to the sea / ocean, I found that Fiume Magra is incorrectly marked as coastline (see here: OSM Inspector | Geofabrik Tools ). Not sure if this is the right place, but I’d like to request this to be fixed.
Thx
László
thank you for noticing. I tried to improve it by removing long stretches of coastline inland, but keeping a few kilometers (estuary), I am not a local and websearch suggested the influence of the sea is at most about 8-9km from the mouth. Feel free to improve it further if you have more accurate information (altough the nature of an estuary is that the saline concentration changes gradually, so there is no hard line in general in these situations).
Thank you for the quick action. Although I’m not a local either, but based on how other similar sized rivers’ estuaries are handled, I’d say that the best would be to change the full length of the river to river area.
That would be plainly wrong. Estuaries belong to the coastline. If maritime parts of some rivers are not tagged as coastline, it should be corrected, not the opposite way.
Do you mean that the following rivers are all mapped incorrectly?
Arno: water color is changing at Ponte della Ferrovia, downstream vessel are for the navigation on the sea.
Note the suburb name: Porta a Mare (Gateway to the Sea).
So yes it needs some tuning.
Serchio: unsure, I don’t see any dock or similar at the current limit Fiume Morto Nuovo, a color change is seen upstream. Connected to a canal, region with almost no tides, it could be correct (see Esri World Imagery (Clarity) Beta: sand and sediments seem to go there).
Clutha River: not only the coastline needs improvement, like here. Unsure where to but the limit.
Cook River: unsure here: not much tides there either.
Hi everyone,
I’m from the Massa-Carrara area and I’m planning to visit the site once my car has been repaired, or as soon as I have some free time.
I hope you’ll forgive my limited knowledge on the subject, but I’d like to better understand how one can determine whether a body of water is part of the sea or a river.
Could anyone explain what indicators or methods are typically used to verify this?
Thank you in advance for your help.
This text has been rephrased from an AI since my vocabulary in english is not very unlimited.
salinity is an indicator, also if the level is influenced by the tides (which are generally not very high in the mediterranean)
Thanks for the explanation for the reformulation (that’s a reasonable usage).
First : the coastline defines the upper limit of the maritime influence. The rivers goes the other direction, down to the low-tide limit. The current river limits are probably fine(well it should go down to the mouth). The issue is with the coastline.
Second, that the basics.
Here we go in more details: Coastline - OpenStreetMap Wiki
The upper limit is in OpenStreetMap the Mean high water springs (MHWS) – The average of the two high tides on the days of spring tides. Self-explaining, isn’t it? 
Mean high water springs (MHWS) is the averaged highest level that spring tides reach over many years (often the last 19 years). Within this, to ensure anomalous levels are tempered, at least two successive high waters during the highest-tide 24 hours are taken.[16]
Such a local level is generally close to the “high water mark” where debris accumulates on a tidal shore on about two days six months apart (and nearby days) annually. The levels are local as some places are nearer to or form places of almost no tides in and around each ocean (amphidromic points).
Source: Chart datum - Wikipedia
Depending on country, the coastline on official maps may use HAT (Highest astronomical tides, like France), MHWS, MWS (Mean water spring). The country may publish the sea-land limits (including in the rivers). France does. italy maybe as well.
A good source for MHWS in Europe is EMODnet Bathymetry, I’ve selected MHW and OSM, so you see the difference.
You may check on ENC IT400115 (electronic navigational chart - Approach to La Spezia) or 115 INT 3364 (paper chart - Litorale della Spezia) where the put the limit (check for copyrights, probably you should use this source only for verification).
For the estuary you can also check the direction of the river, the salinity, the plants growing, nothing 100 % sure. Some information may be public (salinity limit for instance).
You may have specific laws for maritime coast, so you may see that a commune being considered as coastal, you have to have some coastline there.