It's not so much you should use your charts with a "grain of salt", as
you need be aware that they are not perfect and if you have any doubts,
you should use ALL means at your disposal, especially the "Mark I eyeball".
If you see discolored water, obvious current swirls, disturbed wave
action, (to name some) in a particular area, or your wake changes and
you bog down ..... these are indications that something may not be as
the chart suggest, and it doesn't matter whether you're using GPS,
celestial, radar, etc., for your navigation, you may want to stop or
reverse direction till you can figure things out or find a better route.

otn