Edit Sat 2/10: Most of the RER C stations within Paris have reopened, except for
-- St Michel Notre Dame
That is, you can not get on or off the RER C at that station.
You can still take the RER B there or get on the RER B there.
-- Pont de l'Alma (which is closed long term for construction anyway)
EARLIER MESSAGE:
As of today, and until the waters descend, the stations of the RER C that are within Paris are closed (the RER C in Paris runs alongside the Seine and is susceptible to flooding in these situations).
Stations affected (that is, you can not take the RER C at these stations -- other lines are fine at these same stations):
- Saint-Michel
- Notre Dame
- Musée d'Orsay
- Invalides
- Pont de l'Alma (closed anyway for construction until early 2019)
- Champ de Mars
- Avenue du President Kennedy
- Boulainvilliers
To replan a route involving the RER C (for example, to get to VERSAILLES), use the RATP trip planner
You can also check the Twitter feed of the RER C line (in French) for updates, they are very good about keeping announcements up to date:
@RERC_SNCF
The general place to check "perturbations" (disturbances, whether closures or other problems):
https://www.ratp.fr/infos-trafic
And, if you have the CityMapper app on your phone, are using data, and input your favorite lines, it will ping you when there's a problem on "your" line(s)!!